ON THE PIGMENT OF THE NEGRO’S SKIN 
AND HAIR 
BY 
JOHN J. ABEL 
AND 
WALTER S. DAVIS 
From 
THE JOURNAL OF EXPERIMENTAL MEDICINE 
Vol. I, No. 3, 1896 ON THE PIGMENT OF THE NEGRO’S SKIN AND HAIR. 
Br JOHN J. ABEL, M. D., 
AND 
WALTER S. DAVIS, S. B. 
{From the Pharmacological Laboratory of the Johns Hopkins University.) 
Plate XIV. 
1. Introduction, p. I—2.1—2. Earlier work on the pigment of the negro’s skin, 
p. 3—3. Methods of obtaining and cleansing the epidermis, p. 4 
4. Action of reagents on the cleansed epidermis, p. 5—5. Methods of 
isolating the pigmentary granules, p. 7-—6. Possible contamination of 
the pigmentary granules with bacteria and cell fragments, p. 10— 
7. Proportionate amount of pigmentary granules in the dried epidermis, 
p. 11—8. The substratum of the pig-mentary granules, p. 12—9. The 
inorganic constituents of the granules, p. 16—10. Methods of isolating 
and purifying the pigment, p. 21—11. The pigmentary granules and the 
pigment of the negro’s hair, p. 23—12. Alkali-albuminates and peptone- 
like bodies formed by the action of alkalies on the epidermis and hair, 
p. 24—13. Chemical properties of the isolated pigments, p. 26—14. Com- 
bustion analyses, p. 29—15. The iron content of the isolated pig’ment, 
p. 33—16. The origin of the pigmentary substance, p. 35—17. Total 
amount of pigment and of pigmentary granules in the skin of one negro, 
p. 36—18. Function of the epidermal pigment, p. 37—19. Conclusions, 
p. 39. 
1. Introduction. 
The pigments of the animal body constitute a numerous and 
widely distributed class of substances. Almost all of tbe tissues and 
fluids contain more or less pigment either in solution or, wbat is more 
frequently the case, in the form of minute granules of various shapes. 
Copyright, 1896, bt D. Appleton and Company, 2 
On the Pigment of the Negro's Shin and Hair 
Some of tlie pigments that are of great physiological importance— 
haemoglobin and the biliary pigments, for example—have been the 
subject of careful investigation and are fairly well understood with 
respect to their physical and chemical properties, their origin and 
relationships, and the physiological functions which they subserve. 
There are many more pigments of the human body whose chemical 
properties are somewhat known, but whose physiological relation- 
ships are very obscure. As belonging to this class may be named 
the pigments found in melanotic tumours, those of the retinal and 
choroid coats of the eye and of the hair, and the colouring matters 
of serum, of the urine and of fats. 
Another large class of coloured substances is still less understood. 
Of these substances we know at present little more than that they 
exist in this or that tissue of the body; not one of them has been the 
subject of extended chemical research. Instances of these are the 
dark pigments * normally present in the heart, liver, kidney, thyroid 
gland, suprarenal body and testicles, on the peritoneal surface of the 
intestines, in the pia mater and in nerve cells. 
Prominent among these little-known pigments is that found in 
the epidermis of the dark-skinned races. This pigment is of interest 
not alone because it is the distinguishing characteristic of the great 
majority of the human race and because for them it serves a physio- 
logical purpose, but also because of its very probable relationship to 
the pigment more sparingly deposited in the skin of the so-called 
white races and to the dark pigments known as melanins, examples 
of which are found in the hair and in certain malignant tumours. 
Should we reach a thorough understanding of the pigment of 
the negro’s skin, and should this pigment prove to be identical with 
that in the skin of the white races, this knowledge might throw great 
light on many anomalous cases of pigmentation; for example, the 
bronzed skin of Addison’s disease, the brownish patches appearing on 
the face and other parts of the body during pregnancy, the brown or 
black patches sometimes covering large areas of the body and known as 
* Compare Maass, Zur Kenntniss d. kornigen Pigmentes ixn mensclil. 
Kdrper. Arch. f. mikr. Anat., Bd. xxxiv, p. 452. John J. Abel and Walter S. Davis 
3 
nsevi spili, nsevi verrucosi, and nsevi lenticulares, and the lesser pig- 
mentations called freckles. 
Perhaps also closely allied in chemical composition to these pig- 
ments is that which is developed in the course of various chronic 
skin diseases, such as psoriasis, lichen ruber, and xeroderma pigmento- 
sum; also that due to chemical irritation, as after the application of 
mustard or cantharidal plasters or that which follows the repeated 
inroads of clothes lice and other parasites. 
We shall show in the following paper that it is possible to isolate 
the pigment of the negro’s skin, and we believe that the same or a 
similar method will be found applicable to many of the instances of 
pigmentation above enumerated, more particularly to extensive dis- 
colorations of the skin in white persons, as in Addison’s disease. 
2. Earlier Work on the Pigment of the Hegro’s Skin. 
The only work of a chemical nature known to us on the pigment 
of the negro’s skin is found in a brief but suggestive paper communi- 
cated in 1876 to the Chemical News by Prof. J. W. Mallet,* on be- 
half of his pupil Dr. P. P. Floyd, This investigator confined 
himself to a study of the pigment in its crude state—that is, the pig- 
mentary granules plus the cell structure enveloping them. His mate- 
rial was obtained by cleansing with water scrapings of the skin and 
treating them with alcohol and ether to remove the fatty matters. 
Since no attempt was made to isolate the true colouring matter, or 
even the pigmentary granules themselves, the results arrived at are 
of very restricted value. Two instances will suffice to show how in- 
applicable to the isolated pigment is a statement which may be per- 
fectly true of the pigment while still contained in the cells of the 
epidermis, f Floyd says that the “ colouring matter ”is insoluble in 
dilute alkalies, but we found the purified pigment to be soluble in the 
most dilute alkalies or alkaline carbonates or even in distilled water, 
provided only that the pigment used has been recently precipitated. 
*On the Chemical Character of the Pigment of the Negro’s Skin. Chemical 
News, 1876, vol. xxxiv, p. 179. 
t The term pigment-granules in Floyd’s paper can only be construed to 
mean the pigment-bearing cells of the rete mucosum. On the Pigment of the Negro's Skin and Hair 
4 
Again, the main point in Floyd’s paper and the one for which he has 
been widely quoted is his conclusion regarding the iron content of 
the pigments. This point, however, can not be settled by an analysis 
of strips of cuticle. On incinerating strips of dried cuticle taken 
from both black and white cadavers, he found that the ash from the 
former weighed approximately twice as much as that obtained from 
an equal quantity of the latter, and that it contained approximately 
twice as much iron. From this he concluded that in all probability 
the pigment of the negro’s skin is a chemical modification of the red 
colouring matter of the blood. But it must be remembered that 
ferruginous, colourless compounds of a proteid character are present 
in every cell, and on that account no conclusion as to the iron con- 
tents of the pure pigmentary substance can be reached by Floyd’s 
method. We shall show later that in the process of purifying the pig- 
ment, the amount of iron steadily decreases with the removal of the 
adherent inorganic compounds till only the slightest traces of this 
element are left—so small an amount, indeed, that we have concluded 
that the pure pigment contains no iron as a constituent of its mole- 
cule. 
3. Method of obtaining and cleansing the Epidermis. 
The method of obtaining the cuticle in which the pigment is 
lodged varies according to the state of the cadaver. When it has 
lain for some time in contact with aqueous fluids, the epidermis may 
easily be peeled off in large patches from the underlying corium and, 
what is a further advantage, many of the hairs remain embedded in 
the corium. Or the entire skin is first removed and then cut into 
pieces of manageable size and scrubbed with a stiff brush under a 
forcible jet of water, after which each piece is held for a few minutes 
under boiling water and then immediately subjected to a stream of 
cold water, a process which it may be necessary to repeat once or 
twice. The consequent expansion and shrivelling results in a separa- 
tion between the rete mucosum and the underlying corium, and 
when the pieces are stretched out and fastened on a board the entire 
epidermis can be removed with ease, much as a piece of wet paper John J. Abel and 'Walter S. Davis 
5 
is lifted from a table on which it has been flattened out. The corium, 
it may be added, appears perfectly white after the epidermis has been 
removed. 
When these methods of peeling off the epidermis are not possible, 
the following method may be used. Large pieces of skin obtained 
from the dissecting room are allowed to soak for three or four days 
in a five- to seven-per-cent solution of potassium hydrate, after which 
the epidermis is removed by scraping with a nickel spatula. This 
method is inferior to those before mentioned on account of the greater 
difficulty in removing the hairs. 
When a sufficient quantity of epidermis has been collected, it is 
treated first with water, then with alcohol and ether in large ex- 
tractors especially constructed for the purpose. After ten days to 
two weeks of this treatment the shrivelled and dried epidermis has 
become grayish white on its upper surface, the whole appearance 
reminding one of paper made by wasps, and on its lower side black or 
brown according to the amount of pigment contained in it. The 
hairs are now carefully removed, a tedious process requiring many 
days of labour. 
When no more hairs can be detected, the microscope reveals that 
the small white specks with which the lower surface is studded con- 
sist of dried hair follicles in each of which is embedded a minute 
hair. These hair follicles may also be removed with the help of 
broad nickel forceps, but this process requires so much time that it 
was only used in preparing the epidermis for the quantitative estima- 
tion of the pigmentary granules. 
4. Action of Reagents on the Cleansed Epideemis 
The epidermis cleansed as described was subjected to the action 
of various chemical reagents as follows: 
Alkalies.—Dilute solutions of the free alkalies (five to fifteen per 
cent) allowed to act on the epidermis at room temperature for some 
days will disintegrate it, and maceration at water-bath tempera- 
ture brings about a very complete disintegration in a few hours. 
This is, however, no true solution of the pigment, for although a 6 
On the Pigment of the Negro’s Shin and Hair 
large part of the turbid fluid will pass through filter paper with large 
pores, it clears up, if allowed to stand for a day or two, a closely 
packed precipitate being found at the bottom, while the fluid above 
is of a faint straw-colour or ruby-red, according to the strength of the 
alkali used (five to ten per cent) and the length of time it has been 
applied (two to six hours). This black sediment falls out more quickly 
if the fats have been thoroughly removed from the epidermis before 
maceration. 
Even prolonged boiling with ten- to twenty-five-per-cent solutions 
of the alkalies extracts but very little of the pigment. Whatever 
the strength of the alkaline solutions used, the supernatant fluid, on 
being filtered and neutralized with an acid, throws down a precipi- 
tate that is found to contain a great deal of proteid matter which is 
presumably an alkali-albuminate with the admixture of a little pig- 
ment. 
If the black precipitate that settles out from the turbid fluid as 
above described is collected on a flat filter and washed with a very 
weak solution of acetic acid, it will be found to consist of minute 
black or brownish granules which resemble the pigmentary granules 
seen in the lower cells of the cuticle in a microscopic section of the 
skin. Although the granules are thus resistant toward even strong 
solutions of the free alkalies, they dissolve readily in weak solutions 
of the alkalies under a steam pressure of 150° to 160° C. Thus it 
was found that when scraps of cleansed epidermis are heated in a 
sealed tube with a five-per-cent solution of potassium hydrate for a 
few hours at the above temperature, a clear black fluid is obtained 
which passes through filter paper with great ease and can be diluted 
with water to any extent without causing a precipitate. The addition 
of an acid to this solution throws down a black or brown flocculent 
precipitate which is found to possess the properties of a weak acid; 
it forms very soluble amorphous salts with free alkalies or their car- 
bonates. 
Acids.—With the exception of nitric acid, dilute solutions (five 
to fifteen per cent) of the mineral acids allowed to act at room tem- 
perature do not dissolve out the pigment. Concentrated sulphuric John J. Abel and Walter S. Davis 
7 
acid requires weeks to disintegrate the dried epidermis. Dor the 
first ten days the only effect is to swell the pieces of epidermis and 
bring out all their grooves and ridges. Even after two months thin 
filmy pieces are seen swimming in a dark fluid out of which settles 
no precipitate. 
Concentrated hydrochloric acid is more effective; under its 
action in the course of two weeks all of the pigmentary granules 
have settled to the bottom, leaving the supernatant fluid but slightly 
coloured. 
Concentrated nitric acid and fuming nitric acid are most effective 
solvents of the entire epidermis, the pigmentary granules included. 
After some hours a dark-brown fluid results which, on being freely 
diluted with water, throws down a dark-coloured flocculent precipi- 
tate. This precipitate, washed with alcohol and ether, is found to dis- 
solve with ease in very dilute alkalies, yielding an intensely black 
solution. But if the nitric-acid solution has been allowed to stand for 
some weeks, dilution with water no longer throws down the precipi- 
tate and the solution has in the meantime become almost decolour- 
ized. Boiling the epidermis for a short time with much nitric acid of 
specific gravity 1.19 yields a dark-brown solution which, on the 
further application of heat, turns yellow and becomes finally almost 
entirely colourless. On diluting this solution with water, no precipi- 
tate is thrown down. 
Glacial acetic acid allowed to act for months produces no marked 
changes to the naked eye; under the microscope, however, it be- 
comes evident that certain changes in the cells have taken place, 
for the pigmentary granules are seen with greater distinctness. The 
action of chlorine and other oxidizing agents on the epidermis is the 
same as their action on the isolated pigment, which will be described 
later. 
5. Methods of isolating the Pigmentary Granules. 
From the experiments described in the foregoing pages it will 
be seen that the pigmentary granules of the epidermis must be classed 
with the most resistant and unalterable elements of the body. 8 
On the Pigment of the Negro's Shin and Hair 
Por the purpose of learning what substances enter into their com- 
position, we proceeded to isolate them by the following methods: A 
given weight of the epidermis, varying from 10 to 160 grammes, 
cleansed as before described, even the dried hair follicles being for 
the most part removed, was submerged in not less than twenty times 
its weight of a five-per-cent solution of pure potassium hydrate con- 
tained in large nickel bowls placed on the water bath. 
The water in the bath was kept actively boiling, and the pieces of 
epidermis were for the first half hour constantly stirred with a nickel 
spoon; under these conditions the disintegration of the epidermis 
proceeded at a rapid rate, at the end of half an hour only very small 
particles remaining undissolved. 
From time to time water was added so that the concentration of 
the solution should not go above five or six per cent. If after this 
process has been carried on for six hours the nickel bowl be set aside 
for twenty-four hours, there will be found in it a supernatant fluid of 
light-reddish-brown colour and a dense, black powdery precipitate 
consisting of the pigmentary granules. 
Microscopical examinations were frequently made in order to fol- 
low the gradual disintegration of the epidermis step by step until 
there remained only minute brownish particles, not to be clearly dis- 
tinguished except with the help of an immersion lens. 
In Plate XIY, Pig. 1, we have given a drawing of a single cell 
detached from its neighbours showing the appearance of the gran- 
ules. Pig. 2 represents the state of the disintegration after the po- 
tassium hydrate has acted on the epidermis for about two hours and 
a half. It will be seen that all cell outlines have been destroyed, the 
granules adhere together, forming brown or black lumps in each of 
which the individual granules are easily detected, and now and then 
a small aggregation of granules has a contour suggestive of the origi- 
nal cell form. Pig. 3 represents the condition after six hours of 
maceration. Light pressure on the cover glass causes the granules to 
fall apart and to appear in the field as discrete but very minute light- 
brown particles. As to the shape of these granules, we have concluded 
that they are rather elongated than round; this, however, can only John J. Abel and Walter S. Davis 
9 
be determined by examining them under an enlargement of a thou- 
sand diameters or more and under favourable circumstances. The 
traces of foreign matter that may still be detected among the granules 
after long maceration may be removed by washing with warm hydro- 
chloric acid, alcohol, chloroform, and ether. Thus treated, dried, 
and powdered, the granules cohere into little black lumps, as shown in 
Fig. 4. Rubbing up some of this powder with dilute alkalies gives 
us the picture under the microscope of individual granules, as seen 
in Fig. 3. 
A few yellowish ovoidal and globular particles seen here and 
there were at first assumed to consist of a substance related to kerato- 
hyalin, but their inability to take up methylene blue and their disap- 
pearance in hot ether and hot alcohol show that they consist of fat. 
Small irregular black lumps and long black rods that were now and 
then found among the granules were shown by check experiments 
with pure keratin to consist of nickel sulphide. This is formed by the 
sulphur which is split off from the keratin acting on the nickel of the 
bowl and forming a thin coating of nickel sulphide, which breaks 
up into singular and varied forms. 
Another and very simple method of isolating the pigmentary 
granules consists in the use of concentrated hydrochloric acid, which, 
as already described, entirely dissolves the epidermis excepting only 
the granules, which fall to the bottom as a black sediment. Treat- 
ment with so powerful an agent may remove from the granules much 
of their inorganic matter, but when it is desired to isolate the pig- 
ment itself rather than the pigmentary granules, this method promises 
to be of service because it enables us to isolate with ease any desired 
quantity of the granules, no matter how large. 
The black granules, prepared by either of the above methods, 
washed and dried, become a snuff-coloured powder, not to be distin- 
guished in appearance from that yielded by the pigment itself when 
it has been isolated from the granules. 
But, as we shall see later, these two powders differ markedly in 
their behaviour toward reagents. 10 
On the Pigment of the Negroes Shin and Hair 
6. Possible Contamination of the Pigmentary Granules with 
Bacteria and Cell Pragments. 
It might be supposed that the black precipitate described by 
us as consisting of the ultimate pigmentary granules would be found 
to be much contaminated with bacteria. Such is not the case, how- 
ever. The usual methods of staining have failed to indicate their 
presence in sections of the dried and cleansed epidermis, and the fol- 
lowing experiments were made to determine whether bacteria can 
retain their structural integrity when macerated in a five- to six-per- 
cent alkaline solution at water-bath temperature. In the first experi- 
ment 5 grammes of dried tubercle bacilli (pure culture) were sus- 
pended in Y5 cubic centimetres of a five-per-cent solution of potas- 
sium hydrate contained in a small flask which was attached to a 
reflux condenser, and the mixture was then heated for four hours on 
an actively-boiling water bath. At the expiration of this time no bac- 
teria could be detected either on direct examination of the resulting 
turbid fluid or by staining some of the precipitate thrown down by 
alcohol. 
Nothing remained but amorphous flakes and stringy masses. 
A like negative result was obtained when scrapings from culture 
tubes containing the staphylococcus pyogenes aureus were subjected to 
the treatment just described. Nencki and Schaffer * have also shown 
that certain putrefactive bacteria (names not given) are largely dis- 
solved when treated on the water bath with only 0.5-per-cent potas- 
sium hydrate, an insoluble, structureless residue remaining. Con- 
tamination of the pigmentary granules with bacteria must therefore 
be entirely excluded. 
Neither can there be an admixture of cell fragments, for in the 
granules that have been collected on flat filters, washed with hot 
two-per-cent potassium hydrate, water, hot five-per-cent hydrochlo- 
ric acid, hot alcohol, chloroform, and ether, the microscope fails to 
detect any but the merest traces of matter, excepting only the nickel 
sulphide obtained from the bowls. This statement is also confirmed 
* Review in Jahresb. d. TMer-Chemie, Ed. ix, p. 385. John J. Abel and Walter S. Davis 
11 
by the fact that the iron reaction (HCI and K4FeCy6) can now no 
longer be obtained. 
But the most conclusive proof that no foreign matter of organic 
nature lies between the granules is found in the fact that from a 
given weight of granules an amount of crude pigment may be ob- 
tained by the method soon to be described whose weight equals that 
of the granules minus their ash. In other words, the crude soluble 
pigment with properties so different from the granules contains 
everything that they contain, barring only their great excess of ash. 
The force of the above statement will become more apparent 
when we note the method of disrupting the granules, presently to be 
described, for the reagents used for this purpose are the very ones 
that have already done their work in dissolving out foreign organic 
matter. 
7. Proportionate Amount of Pigmentary Granules in the 
Dried Epidermis. 
Ten grammes of cleansed epidermis from which even the hair 
follicles had been removed were macerated for six hours in a nickel 
bowl as just described. 
The pigmentary granules were then collected in two portions on 
small flat filters, washed with a warm, dilute solution of potassium 
hydrate, then with alcohol containing a very little acetic acid until 
the potassium hydrate, as shown by the flame test, was entirely re- 
moved, then with hot alcohol, hot chloroform and ether, and dried at 
110° C. to constancy of weight. 
The amount of pigmentary granules on the one filter weighed 
0.2120 gramme, on the other 0.1089 gramme. The total residue of 
pigmentary granules, therefore, equaled 0.3209 gramme. Prom this 
amount we must subtract 0.0121 gramme as consisting of sulphide 
of nickel, leaving 0.3088 gramme of pigmentary granules. The 
granules would, therefore, constitute 3.08 per cent of the epidermis 
when cleansed as described. 
In a second experiment 9.77 grammes of carefully prepared epi- 
dermis from various parts of the body was treated in the same man- 12 
On the Pigment of the Negro's Shin and Hair 
ner, except that the process of maceration was carried on in a porce- 
lain instead of a nickel bowl. In this case the pigmentary granules 
obtained weighed 0.3693 gramme. 
Neglecting the trifling weight of contaminating material that 
was derived from the porcelain bowl, we find the proportion of gran- 
ules somewhat higher—viz., 3,78 per cent. It is well known that the 
epidermis varies in thickness in different parts of the body, and the 
difference in the above results is therefore easily accounted for. 
8. The Substratum oe the Pigmentary Granules. 
We believe that a perusal of the following pages will leave no 
doubt that the pigmentary granules which settle in the bowls when 
the epidermis is macerated in warm solutions of potassium hydrate 
are no other than the pigmentary granules that may be seen under 
the microscope in every cross-section of the negro’s skin. We grant 
that we must remain in ignorance as to whether the long maceration 
necessary to free the granules from the cells in which they are lodged 
may not have extracted from the granules themselves some constitu- 
ent of a proteid or keratinoid character. It would appear probable, 
however, that had this been the case, the granules would have fallen 
to pieces as do bacteria when their soluble proteids are removed from 
them by treatment with hot alkalies. 
We must also concede it to be possible that the water, alcohol, and 
ether used have removed from the granules some constituent soluble 
in these agents, but this error, if it be such, is unavoidable. 
We have already alluded to the fact that the granules become 
somewhat translucent and pale after long treatment with hot alkalies. 
This change becomes very apparent when microscopic sections of 
healthy skin taken from a living subject are thus treated on the warm 
stage and examined from time to time. This has been kindly done 
for us by Dr. T. C. Gilchrist. Dr. Gilchrist has watched under the 
microscope the sections during the different stages of their disinte- 
gration under the action of alkalies of varying strength, and has 
demonstrated that the granules remaining are those originally de- 
posited in the epidermis. John J. Abel and Walter S. Davis 
Post * has also made this observation, for he says that the ele- 
mentary granules are seen as pale, somewhat swollen rods when they 
have been decolourized f by concentrated potassium hydrate which 
has been allowed to act on them at room temperature for some weeks. 
Are we to conclude from these observations that the pigmentary 
substance is lodged in a substratum of a different character, that there 
is a ground substance which constitutes, so to speak, the body of 
the granules and which is permeated with the pigment? In other 
words, are we to look upon these granules as a kind of trophoplast, like 
chlorophyll granules, and like them composed of a substratum of pro 
teid matter which is stained with a pigment? 
It appears that histologists who have given attention to the sub- 
ject incline to this latter view. W. v. JSTathusius, for instance, 
has recently shown in his paper on the fibrillary structure of the 
keratinoid cells of the fibrous coat of hairs that these cells may be 
so far disintegrated with warm ammonia as to leave undissolved 
their pigmentary granules, lying for the most part in rows as origi- 
nally deposited in the cells, but deprived of some of their pigment 
This investigator also furnishes drawings of the granules arranged 
in rows in the isolated fibrils, their natural pigment removed, and 
methyl violet or fuchsin substituted. 
Still other evidence that there is present in these granules a non- 
pigmented substratum is presented by Peinke, who has recently sought 
to establish the histological similarity of these structures to the tropho- 
plasts of the botanist. Peinke has found that the pigmentary gran- 
ules of the peritoneal cells of the larva of the salamander may be 
bleached with hydrogen peroxide and then stained with safranin. He 
concludes as follows: “ Inasmuch as the pigmentary granules can 
* Virchow’s Archiv, Bd. cxxxv, p. 493. 
t Post evidently does not use “ Entfarbung ” in its literal sense. In onr 
experience, potassium hydrate never entirely removes the pigment unless the 
granules have first been subjected to an acid. 
$ Arch. f. mikr. Anat., Bd. xliii, p. 153. In the explanatory remarks devoted 
to the drawings v. Nathusius refers to detritus lying among the fibrils. We 
must therefore assume that the ammonia leaves much undissolved matter 
in addition to the fibrils and granules. 
# Arch. f. mikr. Anat., Bd. xliii, p. 393. 14 
On the Pigment of the Negro's Shin and Hair 
be freed of pigment and again coloured with a staining dye, it would 
appear to be a justifiable conclusion that tbe substratum of the gran- 
ules is something different from tbe pigmentary substance.5’ 
"We must say, however, that Reinke’s argument does not seem to 
us conclusive. The substance constituting the pigment may have 
been left in situ after having been bleached by the hydrogen peroxide 
and the substance that took up the new dye may be no other than the 
original pigmentary substance itself. In a word, Reinke has not 
proved that the hydrogen peroxide removes anything from the gran- 
ules. 
ISTo objection can be made, we think, to the following method 
of demonstrating that there is in these granules a substratum of a 
non-pigmentary character. Some of the granules isolated and puri- 
fied as already described are macerated for a week or ten days at 
room temperature with a large excess of hydrochloric acid of five 
per cent. The flask containing the granules and the acid is shaken 
a few times a day, and every second day the acid is poured off and 
fresh acid added. At the end of the time the granules are washed 
free of acid with the help of a suction pump or a centrifugal machine, 
and are then treated on the water bath with dilute (two- to five-per- 
cent) potassium hydrate. An astonishing change has taken place; 
the granules now yield up their pigment in large amount to weak 
alkalies and a fluid of a deep-brown, almost black, colour may be 
filtered off in a short time. 
When examined under the microscope, immediately after the 
coloured substance begins to leave them, the granules may still be 
detected as mere shades of their former selves. 
Soon, however, only faintly coloured debris is left, as when bac- 
teria are similarly treated. This debris must originate in the pigmen- 
tary granules, and it can represent nothing else than the substratum 
of Reinke and others. 
We have attempted to stain the granules just as they were begin- 
ning to give up their black pigment to the potassium hydrate. This 
would have made the proof of a separate substratum absolutely 
complete, for we should have had on the one hand the clear, black John J. Abel and Walter S. Davis 
15 
solution, and on the other the minute elements coloured with the 
artificial dye. But after being treated with potassium hydrate, the 
ground substance seems incapable of taking up the new dye. We 
tried, therefore, another method. After the treatment with cold hy- 
drochloric acid of five per cent, a small quantity of the granules was 
placed in a glass tube with a mixture of one volume of alcohol and six 
volumes of concentrated ammonia. The tube was sealed and then 
kept in a water bath at 100° C. for six to ten hours. This process 
extracts from the granules a little of their pigment and they will then 
take up gentian violet with avidity, as seen in Plate XIY, Pig. 5. 
The certain presence of a non-pigmented ground substance in the 
pigmentary granules has led us to inquire whether it would not be 
possible to isolate from white epidermis and white hair minute ele- 
ments which would correspond in every particular, except colour, to 
the black granules of the negro’s skin and hair. We therefore sub- 
jected to the treatment already described such structures as white 
horn, white hair of the dog and of the rabbit, merino wool, and scales 
of epidermis from a person afflicted with ichthyosis. We found that 
white horn dissolved in five- to ten-per-cent solutions of warm potas- 
sium hydrate to a perfectly clear fluid. The other keratinoid struc- 
tures yielded varying small amounts of a highly resistant proteid. 
We have boiled this substance for four hours with a five-per-cent 
solution of hydrochloric acid with the result that only a part of it 
went into solution, and if the substance be again subjected to hot 
potassium hydrate of five per cent, only a little passes into solu- 
tion. In short, even the alternate application for a long time of boil- 
ing alkali and acid does not entirely dissolve this resistant proteid. 
We assume this body to have properties very like that of the ground 
substance of the granules, and if this assumption be correct, it ex- 
plains why it is so difficult to remove from the pigment all traces of 
the contaminating ground substance. Of all the keratinoid structures 
just referred to, white hair from the dog is the most resistant to alka- 
lies and appears to contain the largest proportion of the unknown 
proteid. 
As the quantity of this proteid is in any case small, a large amount 16 
On the Pigment of the Negro's Skin and Hair 
of material is necessary, and most of our experiments were made on 
merino wool. 
We shall soon publish the results of our observations on the 
chemical properties of this hitherto overlooked proteid. We may 
say that by our present method of macerating merino wool and the 
other keratinoid structures with potassium hydrate this resistant pro- 
teid is left behind, not as white granules, but as an amorphous com- 
pound. After isolating the proteid just referred to, we found that 
v. Hathusius* has shown that when white hair is treated with a boil- 
ing aqueous solution of methylgreen, minute, deeply coloured particles 
may be detected which correspond in size and in position to the “ air 
spaces ” of Kolliker in white hair and to the pigmentary granules in 
coloured hair. Yon Nathusius therefore concludes that the same 
histological element is present in both white and black hair, differing 
in the latter case only in its pigment. 
9. The Inorganic Constituents oe the Pigmentary Granules. 
Having seen that the pigmentary units may be isolated in any 
desired quantity, it becomes of interest to learn what inorganic con- 
stituents enter into their composition. This problem is, furthermore, 
one of physiological importance, as bearing on the broad question of 
the distribution and localization of the inorganic constituents of the 
body. 
Humerous difficulties have been encountered in the analysis of 
the granules obtained from the epidermis. Their ash content is found 
to be too high, when they are not washed with hydrochloric acid, to 
remove the amorphous material which appears to be precipitated 
among them by the alkali used. This material promptly gives an 
iron reaction with HCI and K4PeCy6—a test which was applied in 
vain to the granules. This foreign material may readily be removed 
by washing the granules with hot hydrochloric acid of two to five 
per cent; but this process deprives the granules themselves of some 
of the inorganic matter properly belonging to them. We have in- 
cinerated the granules both before and after washing with hot hydro- 
* Log. cit., p. 152. John J. Abel and Walter S. Davis 
17 
chloric acid, and find that in either case an error is introduced into 
the analysis, the total ash being too large in the first and too small 
in the second. The true value lies somewhere between the two. In 
the case of the hair granules soon to be described, the ash content 
obtained by incineration without previous washing with hydrochloric 
acid gives, in our opinion, a correct value, because no foreign matter 
appears to be precipitated upon them. 
Stating for the present the results of our analyses in round num- 
bers, we find that the inorganic constituents of the pigmentary gran- 
ules of the hair dried at 110° C. without previous washing with 
hydrochloric acid make up rather more than eleven per cent of their 
weight. Washed with hydrochloric acid of five per cent, their ash 
content still amounts to nearly seven per cent. 
The pigmentary granules of the epidermis dried at 110° C. with- 
out previous washing with hydrochloric acid show an ash content of 
twenty-six per cent. After thorough washing with hot hydrochloric 
acid this percentage is reduced by one half. 
The great difficulty of entirely removing all adherent foreign mat- 
ter from the epidermis of a cadaver causes us to view with suspicion 
this very high ash content of the epidermal granules, and we can not at 
the present writing assert positively, as we can for the ash content of 
the hair, that no foreign inorganic matter was present. But, as has 
been described, the greatest pains was taken to cleanse the skin thor- 
oughly, and the results we give are taken from several accordant 
.analyses. 
The acids present in the granules are silicic, sulphuric, and phos- 
phoric; the bases * are calcium, magnesium, and iron, the order of 
statement representing the relative amounts. Treatment of the gran- 
ules with hot hydrochloric acid of five per cent reduces the salts of 
sulphuric and phosphoric acids to a low figure, only about ten per 
cent of these constituents remaining, while the percentage of silicic 
acid is but little affected. Iron constitutes over four per cent of the 
* A little aluminium oxide ’was also found in the ash from both kinds of 
granules. We must, however, reserve for a later paper the question whether 
•a small amount of aluminium is contained in the human epidermis and hair. 18 
On the Pigment of the Negro’s Shin and Hair 
ash of the epidermal granules when these have not been washed with 
hydrochloric acid, or about one per cent of the dry granules. 
A trace of this element is retained by the granules with great, 
tenacity in spite of repeated treatment with hydrochloric acid; but, 
as we shall see later, iron does not constitute an integral part of the 
molecule of the pigment. 
That silicon is present in the pigmentary granules of both the skin 
and hair, we can have no doubt. As found by us in the granules of 
the hair, for example, no foreign source can be claimed for it when 
we state that the hair was cut for us from the heads of clean negroes 
in the hospital wards; that it was most carefully picked over and 
washed with hot water, alcohol, and ether; that it was macerated 
in nickel bowls, and the granules collected on flat filters placed on 
perforated porcelain plates in glass funnels, the sides of the filters pro- 
jecting upward along the wall of the glass funnels, so that the gran- 
ules themselves were hardly in contact with the glass, and the silicates 
taken from the glass by the alkaline fluid would all be carried into, 
the filtrate. Besides, the amount of silicon found is too large to be 
derived from the glass funnel, even if no care had been taken. A 
conclusive proof that silicates are present in the granules of both the 
epidermis and the hair, and that they pass into solution along with 
the pigment and adhere to it with great tenacity, is seen in the fol- 
lowing fact. It is possible, as we shall see, to prepare from the epi- 
dermis a specimen of soluble pigment that shall contain no less than 
twelve per cent of ash, including the silicates. Such a pigment will, 
nevertheless, remain in solution in alcohol of eighty to ninety per 
cent for an indefinite period, provided only that a freshly precipitated 
pigment be used. But silicates that have been dissolved out of uten- 
sils of glass and porcelain by alkalies, when added even in small 
amount to an alcoholic solution of the pigment of the strength re- 
ferred to, fall out promptly, as we found by actual trial, and carry 
down with them considerable pigment. 
The above furnishes one of several proofs of the close union that 
exists between the substratum of the pigment and the inorganic con- 
stituents of the pigmentary granules. Other instances of this condition John J. Abel and Walter S. Davis 
19 
are seen in the firm union that exists between the proteids of the body 
and the mineral compounds accompanying them.* In the vegetable 
world we find the same close connection existing between cellulose 
and mineral compounds, like silicates of iron and calcium. Small 
quantities of inorganic material still adhere to cellulose, even after 
repeated solution in ammoniacal cupric oxide and repeated pre- 
cipitations and washings with hydrochloric acid, thus furnishing 
a striking reminder of the readiness with which our pigment re- 
mains in solution in alcohol, notwithstanding the considerable quan- 
tity of adherent mineral matter. Lange f concludes, as the result of 
his experiments in this field, that the mineral constituents which can 
not be entirely removed from cellulose are distributed in the mem- 
branes of the cell as particles of an insoluble compound of the ele- 
ment in question; and when the membranes are dissolved, these min- 
eral compounds are held in suspension in the solution, and filtering 
holds back only a portion. Some such hypothesis may also explain 
the “ close union ” referred to above as existing among the constitu- 
ents of the pigmentary granules. 
That silicon should be found in the pigmentary granules of both 
the epidermis and the hair need not occasion surprise. Silicon has long 
been known to be one of the constituents of hair; it has also been 
found in the epidermal scales from a person afflicted with ichthyosis, X 
and traces of it exist in the urine. It is found to a considerable extent 
in the ash of feathers, and Henneberg # has found it in the blood 
of chickens to the amount of 0.0139 per cent. It is very probable 
that silicon may be proved to be an indispensable constituent of the 
integumentary structures, more especially of their pigmentary 
granules. 
As to the function of these inorganic constituents, we can only 
offer surmises. It may be that they serve the purpose of a mordant, 
enabling the substratum of the granule to hold and “ fix ” the solu- 
* Cf. M. Hencki, Bemerk. iib. d. sogenannte Asche d. Eiweisskdrper. Arch, 
f. exp. Path. u. PharmaTtol., Bd. xxxiv, p. 334. 
t Ber. d. deutsch. chem. Gesellsch., Bd. xi (1878), p. 826. 
f Halliburton, Chemical Physiology and Pathology, p. 566. 
* Ann. d. Chem. u. Pharm., Bd. Ixi (1847), S. 257. 20 
On the Pigment of the Negro's Skin and Hair 
ble pigment.* Closer study of this interesting question may perhaps 
furnish an insight into nature’s method of dyeing. We have already 
said that it is only possible to dissolve the granules in weak alkalies 
at water-bath temperature when they have first been subjected to 
maceration with hydrochloric acid. ]STow, it can be easily shown that 
the acid removes only inorganic constituents from the isolated gran- 
ules, and it would therefore seem that the presence of this inorganic 
matter is in some way essential to the retention of the pigment, since 
its removal renders the granules soluble in a medium which before 
failed to dissolve them. 
The ash content of the granules remains high, even if large de- 
ductions are made, as in the case of those derived from the epidermis. 
Our analyses are verified in this respect by one made many years 
ago by Scherer, t who includes in his analyses of proteids that of the 
pigment called by him the pigmentum nigrum oculi. To obtain it, 
the black pigment-bearing cells of the choroid coat of oxen’s eyes were 
brushed off with camel’s-liair brushes under water, allowed to settle, 
and were then strained through a filter of linen cloth, in order to re- 
move any fragments of tissue; the inky-black filtered fluid was then 
evaporated, and the residue extracted with boiling alcohol and ether, 
and dried; 0.345 gramme of the dried substance gave 0.035 gramme 
of ash, or 10.1 per ln Scherer’s analysis the entire pigment- 
bearing cells of the choroid coat were incinerated; but had he iso- 
lated and analyzed the granules themselves, we have no doubt the 
ash content would have approximated that found by us in the hair. 
It seems highly probable that all pigmentary granules contain a great 
deal of inorganic matter. 
* Such a theory must, however, take account of the fact that white feathers 
contain fully as much silicon as do those that are coloured, also that the 
feathers of birds living on grains contain more silicon than those living 
mainly on soft fruits. Vide Gorup Besanez, Ann. d. Chem. u. Pharm., Bd. Ixi 
(1847), p. 47. 
\ Ann. d. Chem. u. Pharm., Bd. xl (1841), pp. 1-65. 
\ Scherer gives the ash as amounting to 9.8 per cent, but, according to his 
own figures, it is as above. John J. Abel and Walter S. Davis 
21 
10. Methods of isolating and purifying the Pigment. 
It is only necessary to apply chemical reagents in the proper se- 
quence in order to dissolve out of the grannies the pigment contained 
in them. Thus, if the grannies that have settled out from the alka- 
line macerating fluid be washed free of alkali by decantation, and 
then digested at room temperature with five to ten per cent HCI for 
ten days, the acid being renewed every two days, and, after being- 
washed free of acid, be now again subjected to the action of warm dilute 
alkalies, it will be seen that the alkaline solution becomes at once 
deeply coloured. After some hours of maceration on the water bath 
with five- to ten-per-cent solutions of potassium hydrate, only a small 
residue, consisting largely of inorganic matter, is left undissolved, and 
repeated digestion with ten-per-cent potassium hydrate reduces this 
undissolved residue to trifling proportions. 
Instead of digesting the granules with hydrochloric acid at room 
temperature, the same result may be obtained by boiling them with 
the acid for four hours. This method was used by us only once for 
the special purpose of studying the effect on the iron content of the 
ash. At all other times only cold five-per-cent hydrochloric acid was 
used that we might run no risk of removing iron from the molecule 
of the pigment. 
The black alkaline solution of the pigment is now diluted with 
an equal volume of water and filtered; it remains perfectly clear on 
standing, a minute sediment of finely divided sulphide of nickel being 
found at the bottom of the vessel. In our early work we precipitated 
the pigment out of its first alkaline solution by means of a large excess 
of a mixture of six volumes of alcohol and one of ether. After allow- 
ing the precipitate to settle for some days, the supernatant fluid was 
removed with the siphon, and the dark-brown precipitate was collected 
on flat filters, washed with warm alcohol, to which a little acetic acid 
had been added, redissolved with the help of a trace of potassium 
hydrate or of ammonia, and reprecipitated with alcohol and ether. This 
process was repeated seven or eight times. In the later stages am- 
monia was used to redissolve the pigment, and, after the solution had 22 
On the Pigment of the Negro's Shin and Hair 
been effected, the ammonia was driven away on the water bath before 
the solution was filtered. In such a case the pigment still remains 
in perfect solution after the removal of the ammonia. With the 
gradual removal of the potassium used to effect the first solution, it 
became, however, increasingly difficult to precipitate the pigment 
with alcohol. Finally, it remained in solution in a fluid containing 
not far from ninety per cent of alcohol, and, in order to precipitate the 
pigment, it was found necessary to add considerable acetic acid. This 
fact made it seem probable that the pigment would be found nearly 
pure, but incineration showed an ash content as high as 12.4 per cent. 
We were therefore obliged to abandon this method of isolating the 
pigment, and to reserve the precipitation with alcohol and ether for 
the later stages of the process, after the ash content had been reduced 
by alternate treatment with alkalies and acids. Hirschfeld,* toward 
the close of his valuable paper on the pigment of the choroid coat, 
regrets that he did not sooner observe that an excess of alcohol pre- 
cipitates the pigment, as he might have used this method to isolate it. 
Recently we have proceeded as follows: A large quantity of 
cleansed epidermis—-say 100 grammes—is macerated in a number of 
large nickel bowls with twenty to thirty times its weight of a five-per- 
cent solution of potassium hydrate. After the maceration has con- 
tinued for six hours, the black fluid is poured into a large glass jar, 
and six volumes of alcohol are added. In a day or two a dense black 
precipitate has settled out, while the keratoses and alkali-albuminates 
derived from the epidermis remain in solution.. The black precipitate 
is next subjected to the action of cold dilute hydrochloric acid, as 
already described. The granules are then dissolved in potassium 
hydrate in nickel bowls on the water bath, the solution is diluted with 
water and filtered, and the pigment is precipitated out by the addi- 
tion of acetic acid in excess. After the pigment has settled out, the 
red, supernatant fluid is decanted, and the pigment is collected on 
flat filters and washed free of acid. For this purpose water is at first 
used, but, when the pigment begins to dissolve in the wash water, 
absolute alcohol is substituted. The pigment is now again dissolved 
* Zeitschr. f. physiol. Ghent., Bd. xiii, p. 420. John J. Abel and Walter S. Davis 
23 
in dilute potassium hydrate (two to five per cent), heated in the water 
bath for some hours, and again filtered, when a small residue of in- 
soluble flocks will be found on the filter; it is then again precipitated 
with an excess of acetic acid, allowed to stand as before, collected, and 
washed. It is now dissolved in ammonia, the ammonia driven off on 
the water bath, the solution filtered, and the pigment precipitated 
out with alcohol and ether, to which a very little acetic acid has been 
added. This process is repeated until it is found that the ash con- 
tent has been reduced to one or two per cent. After this, the pig- 
ment is washed with hot alcohol, chloroform, and ether until these 
reagents remove nothing further from it. The ash content is thus 
reduced to a low figure, varying from 0.8 to 1.2 per cent in the in- 
stances where the pigment was purest. 
11. The Pigmentary Granules and the Pigment oe the 
Negro’s Hair. 
While the study of the pigment of the negro’s skin has been the 
chief purpose of our investigation, we have also isolated the pig- 
mentary granules and the soluble pigment of the negro’s hair. Prom 
600 to 1,000 grammes of negro’s hair, cleansed with great care and 
treated with alcohol and ether in large extractors, were macerated in 
large copper kettles over a free flame with ten times their weight of a 
five-per-cent solution of potassium hydrate, care being taken not to 
allow the temperature to rise above 95° C., or the solution of potas- 
sium hydrate to go beyond a concentration of six per cent. The black, 
turbid fluid was then poured into glass jars containing "a large excess 
of alcohol or a large quantity of dilute hydrochloric acid of such 
strength that, when the turbid fluid had been added, the whole should 
have a plainly acid reaction. If alcohol is used, the black precipitate 
is flocculent; if hydrochloric acid is used, the precipitate falls out in 
large lumps that have a sticky feel, because of an admixture with 
an alkali-albuminate of a glue-like character. In this latter mixture 
sulphuretted hydrogen is also given off in large quantities, which is 
not the case when the turbid alkaline fluid obtained from the skin is 
similarly treated. The main constituent of the precipitate in both On the Pigment of the Negro's Shin and Hair 
cases is the pigmentary unit of the hair, a large black, rod-like particle, 
very much resembling in form certain bacteria. Plate XIV, Fig. G 
shows these rods in a piece of crushed hair, which had been macerated in 
hot potassium hydrate for fifteen minutes—a length of time found suffi- 
cient to remove the scaly covering of the hair and soften its fibrous 
substance. Fig. 1 represents the pigmentary granules of the hair after 
treatment in a closed tube with alcohol and strong ammonia, and subse- 
quent staining with gentian violet. 
In order to isolate the pigment of these granules, the black pre- 
cipitate thrown out by alcohol or hydrochloric acid is treated in the 
way already described as applicable to the pigment of the skin. The 
pigment finally obtained is not distinguishable in any way from that 
obtained from the epidermis. As with the epidermis, so also with the 
hair, maceration in concentrated hydrochloric acid in a closed bottle 
entirely dissolves all of it but the granules. Twenty cubic centimetres 
of hydrochloric acid thrown on a few curls of negro’s hair entirely 
disintegrate them in the course of a week. At the end of this time 
the supernatant fluid has a reddish-violet colour, while a black pre- 
cipitate, consisting of the typical granules, has settled at the bottom. 
On account of its convenience, we propose to use this method in future 
work on the pigment of the skin and hair. 
To our great surprise, a given weight of hair contains a smaller 
proportion of pigmentary granules than does a like weight of epi- 
dermis. Thus, 10 grammes of negro’s hair yielded only 0.1889 
gramme of granules, or 1.9 per cent, as compared with 3.08 to 3.18 
per cent of granules contained in the epidermis. This result was 
afterward abundantly verified in the isolation of pigment from large 
amounts of hair. 
12. Alkali-albuminates and Peptone-like Bodies formed by 
the Action of Alkalies on the Epidermis and Hair. 
When the alcoholic fluid which is decanted from the granules is 
freed of its alcohol by distillation, and the resulting alkaline fluid is 
made acid, an alkali-albuminate, already referred to as having a ropy, 
sticky character, is thrown out. When the macerating .alkaline fluid John J. Abel and Walter S. Davis 
containing either hair or skin granules is put into weak hydrochloric 
acid, in order to precipitate the granules, this alkali-albuminate at 
first remains in solution, although the fluid has an acid reaction, and 
can be precipitated by the addition of more hydrochloric acid to the 
fluid filtered off from the granules. IST. Sieber * has also called atten- 
tion to this substance in her paper on the pigment of the choroid coat 
and of the hair. In the case of the epidermis, an alkali-albuminate 
is also formed, but its physical properties are entirely different. It 
falls out as a powdery sediment, and does not form a translucent glue- 
like mass on drying, as does the alkali-albuminate from the hair. 
Both of the alkali-albuminates, when collected on filters, washed, and 
dissolved in a little alkali, now fall out immediately on neutralization 
with a mineral acid, not requiring an excess of acid, as they do when 
still mixed with the alkali used for maceration and with the soluble 
products of the epidermis and hair. They also dissolve readily in a 
little hydrochloric acid of twenty-five per cent, and are completely 
precipitated from this solution by the addition of ammonium sulphate 
or sodium chloride. 
We think it highly probable that these albuminates are derived, 
in large measure, from the keratins of the skin and hair by the action 
on them of the potassium hydrate; for Lindwall t has shown that 
when the keratin obtainable from the shell membrane of the hen’s 
egg is treated with sodium hydrate, an alkali-albuminate and peptone- 
like bodies are formed. We may also add that the fluids from which 
the alkali-albuminates referred to have been separated, all promptly 
give the red biuret reaction at room temperature, and, as the fluid no 
longer contains a native proteid or an alkali- or acid-albuminate, it is 
safe to conclude that we have in solution some peptone- or albumose- 
like body in addition to the alkali-albuminate referred to. 
t Beitrage zur Kenntniss des Keratins. Reviewed in Jahresh. d. Thier- 
Chemie, Bd. xi, p. 38. 
* Arch. f. exp. Path. u. Pharmakolßd. xx, p. 364, 26 
On the Pigment of the Negro's Shin and Hair 
13, Chemical Properties of the Isolated Pigments. 
The isolated pigment of the negro’s skin presents the appearance 
of a dark-brown or snuff-coloured powder. If a little of this powder 
is placed upon a strip of blue litmus paper and moistened with a drop 
of water, it gives a markedly acid reaction. If it be heated in a plati- 
num crucible, a mixed odour of burnt horn and pyrrol is per- 
ceived and the pine-sliver reaction for pyrrol is obtained, with such 
promptness and intensity that we must assume this substance 
to be present in considerable quantity among the distillation 
products of the pigment. Toward the close of the incineration the 
odour of pyrrol disappears, and an overpowering odour of hydrocyanic 
acid is given off. Freshly precipitated and washed free of potassium, 
the powder is soluble in water and in a large excess of alcohol of ninety 
per cent. Allowed to stand over sulphuric acid for months, or dried 
to constancy of weight by heating at 120° C., the pigment changes 
from snuff-colour to a dense black, its particles shining like anthracite 
coal. It loses its free solubility in water, alcohol, and dilute alkalies, 
but long-continued digestion on the water bath with strong alkalies 
again dissolves it. 
The pigment is entirely insoluble in the usual organic solvents, 
as ether, chloroform, amyl alcohol, acetone, glycerin, acetic ether, 
xylol, toluol, carbon disulphide, phenol, and pyridine. It is precipi- 
tated from its aqueous solutions by potassium ferrocyanide, copper 
sulphate, ammoniacal zinc chloride, silver nitrate, lead acetate, calcium 
acetate, barium hydrate, and calcium hydrate. The addition of sodium 
chloride, magnesium or ammonium sulphate, and of other neutral salts 
to an aqueous solution induces a complete precipitation of the pigment. 
Alkaline solutions examined with the spectroscope show no absorption 
bands. 
The addition of an acid in excess to the alkaline solutions causes 
the pigment to fall out at once as a brownish-black flocculent precipi- 
tate. Concentrated hydrochloric acid does not dissolve the pigment, 
and appears to have no damaging effect on it, even long boiling with 
a twenty-five-per-cent solution leaving the pigment unchanged. Con- John J. Abel and Walter S, Davis 
27 
centrated sulphuric acid only slowly dissolves a little of the pigment, 
and, when the solution of what little is taken up is dropped into ice 
water, the pigment falls out apparently unchanged. 
Concentrated nitric acid easily dissolves the jDigment, forming 
with it a dense black solution, from which it may be precipitated on 
dilution with water. It may be boiled with this acid or repeatedly 
evaporated with it without loss of colour. Glacial acetic acid does not 
dissolve the pigment. 
Very dilute solutions of the pigment lose their colour when acted 
upon for a few days by neutralized hydrogen peroxide, and dark- 
brown flocks settle out. Chlorine passed into an alkaline solution of 
the pigment immediately deprives it of its colour. When the pig- 
ment is repeatedly evaporated down in a porcelain bowl with nitro- 
hydrochloric acid, there remains a reddish-yellow resinous mass, in- 
soluble in alkalies, water, alcohol, or ether, which dissolves readily 
in amyl alcohol. On evaporation, a reddish-brown resinous mass is 
obtained, the nature of which we have thus far been unable to de- 
termine. 
The behaviour of the pigment toward reagents, as described, 
makes it evident that it is a very resistant substance. This view is 
still further strengthened by the following experiments: 2.6 grammes 
of hair pigment, with an ash content of 2.19 per cent, and a sulphur 
content of 1.7 per cent, was dissolved in 500 cubic centimetres of a 
five-per-cent solution of potassium hydrate, and kept for four and a 
half hours in an autoclave at a temperature of 185° C. At the end 
of this time the black solution was filtered, the pigment thrown out 
with acetic acid, collected, washed, and dried. On examination, it 
was still found to contain much sulphur. It was therefore again 
dissolved in 500 cubic centimetres of a five-per-cent solution of potas- 
sium hydrate, and kept, for three hours at a temperature of 200° C. 
The solution not having changed in colour, it was brought up to a 
potassium hydrate content of thirty per cent, and was again kept for 
two hours at a temperature of 200° C. The black solution was then 
treated in the usual way to recover the pigment. As nearly as we 
could judge, fully one third of the pigment originally put into the 28 
On the Pigment of the Negro's Skin and Hair 
autoclave had disappeared, and the part left had more markedly 
acid properties than before. The recovered pigment was found to 
have a somewhat higher sulphur content. Thus, 0.3551 gramme 
gave 0.0496 gramme of barium sulphate, and therefore con- 
tained 1,9 per cent, of sulphur. Unfortunately, part of the solution 
from which the sulphuric acid was to be precipitated was spilled, 
and there has been no opportunity to repeat the experiment, so 
that we must place the sulphur content somewhat higher. We 
judge it to be in the neighbourhood of 2 per cent. We con- 
clude that the proteid material of the ground substance had been 
decomposed by this treatment, for the odour of skatol became very 
apparent when steam was allowed to escape from the autoclave. The 
recovered pigment no longer emitted the odour of burnt feathers 
on being incinerated, but the presence of nitrogen was nevertheless 
conclusively shown by Lassaigne’s method. The pyrrol reaction could 
no longer be obtained from the vapours emitted on dry distillation. 
This last fact is of importance. The presence of much pyrrol among 
the products of dry distillation of the melanins has led certain chem- 
ists to suspect that these substances are pyrrol derivatives, and we 
ourselves at first held this view. In two trials with a pigment ob- 
tained as above, and in a third trial with a pigment that had been 
heated to 260° C. with a saturated solution of barium hydrate, we 
failed to get the pine-sliver reaction for pyrrol, although a far smaller 
amount of the original pigment gave the reaction unmistakably. The 
vapours given off on burning some of the pigment purified in the man- 
ner just described with barium hydrate are difficult to characterize; but 
the odour of burnt feathers and of pyrrol is certainly not present. 
In the experiment just referred to, in which barium hydrate was 
used to free the pigment from the ground substance, 1 gramme of pig- 
ment was kept at 260° C. with a saturated solution of this agent for 
four hours. After such treatment, this specimen of pigment, as we 
have already noted, failed to give the pyrrol reaction; and, strange 
to say, it was almost entirely precipitated from its solutions in nitric 
acid on the addition of an alkali, even when this solution no longer 
contained any barium. John J. Abel and Walter S. Davis 
We believe that the last-named method furnishes us with a means 
of entirely removing the ground substance from the pigment, and 
it must be left to later research to show with its help whether the 
substance thus obtained is a single chemical individual. 
The substatice obtained when the pigment is heated under pres- 
sure with potassium hydrate is perhaps closely related to the hippo- 
melaninic acid obtained by Berdez and JSTencki,* by fusing with potas- 
sium hydrate the melanin isolated from melanotic tumours of the 
horse. 
It will be seen that we are only at the beginning of a true chem- 
ical knowledge of the melanins of the skin and hair. It would seem 
very probable that the melanins thus far described by investigators 
were all more or less contaminated with the proteid to which we 
have referred. But it is certainly a great advantage to see our way 
to an easy removal of all contaminating substances, and we propose, 
with the help of this method, to continue our investigations into the 
chemical nature of the melanins of the skin and hair. 
14. Combustion Analyses. 
Below are given the results of combustion analyses of pigment 
from the skin and hair prepared in various ways. We are fully con- 
scious of the fact that these analyses do not assist us in establishing 
an empirical formula for our pigment, for the reason that the true 
pigment is still contaminated with the proteid-like substance that 
constitutes the groundwork of the pigmentary granules. Our object 
in making them was to learn whether different methods of preparing 
the pigment and prolonged treatment with strong alkalies really alter 
the so-called isolated pigment, when neither colour nor chemical be- 
haviour have been in the slightest degree affected. Had spectrophoto- 
metric methods been applied, it is probable that they would have sup- 
plemented these analyses in a valuable way, or even have rendered 
them unnecessary. 
* Arch. f. exp. Path. u. Pharmalcol., Bd. xx, p. 359., On the Pigment of the Negro’s Shin and Hair 
30 
Pigment of the epidermis, prepared by repeated precipitation with 
alcohol and ether and a little acetic acid out of solutions in dilute potas- 
sium hydrate, and finally out of solutions in ammonia, from which, how- 
ever, the ammonia had been’ expelled before precipitation by the agents 
named. The special feature of this method is the mild treatment with 
potassium hydrate. The pigments of both the epidermis and hair are 
excessively hygroscopic, so that all weighings must be performed in well- 
closed capsules. 
0.3972 gramme of pigment burned in oxygen current with lead chro- 
mate, finely powdered lead chromate being also strewn on the substance 
in the combustion boat, gave 0.5468 gramme of C02 and 0.1000 gramme 
of H2O. The ash content of this specimen, as determined by previous 
analysis, was 3.17 per cent; calculating for ash-free substance, we 
find that the above specimen contained 51.83 per cent C and 3.86 per 
cent H. 
0.3656 gramme of substance gave by fusion with KOH and KN03, 
after previous oxidation with concentrated nitric acid—the analysis being 
carried out in detail according to the directions of Hammarsten *— 
0.0928 gramme of BaS04 = 3.60 per cent S, calculated for ash-free sub- 
stance. 
0.2065 gramme of substance gave by the method of Dumas 24.7 cubic 
centimetres of nitrogen with the barometer at 759.2 millimetres and the 
temperature 28.5° C. H 0.02802 gramme, or, calculated for ash-free 
substance, 14.01 per cent. 
Hair pigment prepared in the same manner as skin pigment, except 
that it was subjected for a longer time to treatment with potassium 
hydrate. 0.1922 gramme gave 0.0073 gramme ash = 3.79 per cent. 
0.2439 gramme of pigment gave 0.4536 gramme of C02 and 0.0746 
gramme of H2O, or C = 52.74 per cent and H = 3.53 per cent. 
0.8114 gramme of pigment gave 0.1897 gramme of BaS04, the analy- 
sis being carried out as already described for the sulphur analysis of the 
skin pigment. Calculated for ash-free substance, S = 3.34 per cent. 
0.3953 gramme of substance gave by the method of Dumas 34.8 cubic 
centimetres of nitrogen, with the barometer at 760.2 millimetres and 
the temperature 26.5° C. IST 0.03995 gramme; correcting for ash, we 
find N = 10.51 per cent. 
The percentage composition calculated for the ash-free pigment is 
therefore as follows: 
* Zeitschr. f. physiol. Ghent., Bd. ix, p. 289. John J. Abel and Walter S. Davis 
31 
Pigment of the Epidermis. 
C = 51-83 
H = 
3-86 
BT = 
14-01 
S = 
3-60 
0 = 
26-70 
100-00 
Pigment of the Hair. 
C= 52-V4 
H = 
3-63 
N = 
10-51 
S = 
3-34 
0 = 
29-88 
100-00 
It will be seen from the above table that the pigment of the epi- 
dermis differs markedly in its nitrogen content from that of the hair. 
This difference is very likely due to the more prolonged treatment 
with potassium hydrate. We have found that the method of prepara- 
tion has a great influence on the percentage composition of the pig- 
ments, and it seems impossible to prepare two specimens from the 
same original material so that they will give the same analytical 
results. Thus, a specimen of pigment from the epidermis, ana- 
lyzed in the early stages of purification by the alcohol method, 
had the following composition: C = 52.17 per cent. 11 = 4.14 
percent. H = 12.8 per cent. S = 4.02 per cent. 0= 26.87 per 
cent. 
The pigment of both skin and hair was next treated on the water 
bath with a very strong solution of the potassium hydrate, and the 
effect noted. 
A quantity of pigment whose ash content had already been re- 
duced to a low figure was dissolved in a ten-per-cent solution of potas- 
sium hydrate, and this solution was reduced in a nickel bowl on the 
water bath to fifty or sixty per cent in strength. Water was then 
added and the evaporation repeated, and this treatment was kept up 
for six hours. The solution was then diluted and filtered, and the 
pigment precipitated with an excess of acetic acid, after which it was 
collected on flat filters and washed with alcohol until all traces of 
potassium and acetic acid had been removed. The pigment was now 
taken up in ammonia, the ammonia expelled on the water bath, and 
the black solution filtered and precipitated with a large excess of alco- 
hol and ether and a small amount of acetic acid. It was then collected 
on flat filters, washed free of acetic acid with alcohol, and then treated 
with hot alcohol, chloroform, and ether. Thus prepared, the pigment 
of the epidermis has the following composition: On the Pigment of the Negro’s Shin and Hair 
0.1333 gramme of pigment from the epidermis gave 0.0011 gramme 
of ash, consisting of minute dark specks 0.83 per cent. 
0.1139 gramme of another specimen of pigment from the epidermis 
that had not been allowed to stand so long while in a state of solution gave 
0.00143 gramme of ash, consisting of minute black specks = 1.34 per 
■cent. 
0.1570 gramme of pigment from the epidermis gave 0.3044 gramme 
of C02 and 0.0733 gramme of li20. Correcting for an ash content of 1.34 
per cent, we have C = 53.56 per cent and H = 5.11 per cent. 
0.3357 gramme of pigment from the epidermis gave 30.0 cubic centi- 
metres of nitrogen, with the barometer at 767.4 millimetres and a tempera- 
ture of 18° C.; correcting for ash, IST 15.47 per cent. 
0.4136 gramme of pigment from the epidermis gave 0.0750 gramme 
of BaS04; correcting for ash, S = 3.53 per cent. 
0.4170 gramme of pigment from the epidermis gave 0.07006 gramme 
of BaS04. This particular analysis was made with a specimen contain- 
ing 3.34 per cent of ash. Correcting for ash, we have S = 3.36 per cent. 
Pigment of hair treated with strong potassium hydrate as previously 
■described: 
0.3598 gramme gave 0.0057 gramme of a reddish ash 3.19 per cent. 
0.1665 gramme gave 0.34075 gramme of C02 and 0.0799 gramme of 
H2O. C = 57.06 per cent; H = 5.45 per cent. 
0.1646 gramme gave by the method of Dumas 17.6 cubic centimetres 
of nitrogen at 30° C., with the barometer at 758 millimetres. IST 13.87 
per cent. 
0.7337 gramme gave 0.0934 gramme of BaS04. S = 1.77 per cent. 
Placing the results in parallel columns— 
Pigment of Epidermis. 
0 = 
53-56 
H = 
5-11 
N = 
15-47 
S = 
2-53 : 2-36 
0 = 
23-33 
100-00 
Pigment of Hair, 
C = 
57-06 
H — 
6-45 
N = 
12-87 
S = 
1-77 
0 = 
22-85 
100-00 
Comparing the later analyses—that is, after the prolonged diges- 
tion with strong potassium hydrate—with those previously ob- 
tained with the help of less destructive methods, we see that the sul- 
phur content has been considerably lowered for both pigments, and 
the carbon hydrogen and nitrogen content raised. 
We are inclined to believe that this change in the sulphur con- John J. Abel and Walter S. Davis 
tent of the pigments is dne to the fact that the contaminating sub- 
stance derived from the pigmentary granules has been in part decom- 
posed by the potassium hydrate. The fact that it is impossible 
to isolate two specimens of the pigments so that their percentage 
composition does not vary with even slight differences in the method 
of preparation, also points to the conclusion that we are not yet deal- 
ing with a single chemical individual, that our so-called isolated pig- 
ment is a mixture of at least two substances, one of which is responsi- 
ble for this variability. It seems very improbable that this variability 
can be referred to the pigmentary compound, for this retains its col- 
our and its general chemical character, however severe the treatment 
to which it is subjected. 
15. The Iron Content of the Isolated Pigments. 
The pigmentary granule, as we have seen, contains much iron, 
but, as the pigment isolated from these granules is purified, we find 
that the iron content steadily diminishes until but the merest trace 
remains, only to be accurately estimated by the spectrophotometric 
method.* We must therefore conclude that iron is not present as 
a constituent part of the molecule of the pigment; that it does not 
enter into its chemical structure, as does the iron of hsernatin, for 
example, but is present only as an impurity. 
The present diversity of opinion as to the origin and iron content 
of the melanins, of which our pigment is one, is, we must believe, 
owing to the fact that a clear distinction has not always been made 
between the complex pigmentary granule and the pigment itself. 
The former contains iron; the latter does not. 
In support of our view as to the low iron content of the pigmen- 
tary substance, we present, first, analyses of pigment with a relatively 
high ash content, and then analyses showing the ash content reduced 
to a low limit. 
Thus, a specimen of pigment prepared by precipitating its first 
solution in potassium hydrate with strong acetic acid, and then wash- 
* Cf. Morner, Zeitschr. f. physiol. Chem., Bd. xi, p. 87. 34 
On the Pigment of the Negro's Pkin and Hair 
ing the collected pigment thoroughly with this acid, had an ash con- 
tent of 3.3 per cent and an iron content of 0.14 per cent, estimated 
by titration with a weak solution of potassium permanganate. We 
always found this high percentage of iron when the pigment had not 
been repeatedly dissolved and precipitated. 
Another specimen which had been prepared by the method of 
frequently repeated precipitation with alcohol gave the following 
results: 0.3863 gramme yielded 0.0134 gramme of ash, or 3.46 per 
cent. The amount of this ash taken up by dilute hydrochloric acid, 
after first rendering the silicic acid insoluble, was 0.0079 gramme. 
The amount of iron in this solution, estimated by the gravimetric 
method of Ludwig and Gottlieb,* was found to be 0.000385 gramme 
(0.00055 Fe203 obtained). The iron content of the pigment in this 
case was therefore 0.099 per cent. The residue of the ash insoluble 
in dilute hydrochloric acid consisted for the most part of silicon di- 
oxide, and weighed 0.0055 gramme. In this instance we see that 
the iron has been much reduced, although the ash remains high, on 
account of the alcohol method being used. 
A still lower iron content is found in specimens of pigment that 
have been prepared by the method of prolonged treatment with potas- 
sium hydrate, as already explained. 
I. Thus 0.2353 gramme yielded 0.00529 gramme of a black, powdery 
ash. Of this ash 0.00359 gramme passed into very dilute hydrochloric 
acid, after having first rendered the silicic acid insoluble. The iron of 
this amount was found by titration with a weak solution of perman- 
ganate to be 0.00017 gramme, and constituted therefore only 0.076 per 
cent of the pigment. The part of the ash insoluble in dilute HCI con- 
sisted of silicon dioxide and aluminium oxide. 
11. Pigment = 0.1333 gramme, ash obtained 0.0011 gramme, or 
0.82 per cent, and containing 0.00003 gramme of iron, as estimated by 
colour titration with KCNS. This specimen of pigment therefore con- 
tained only 0.02 per cent of iron. 
111. Pigment = 0.1139 gramme; ash obtained = 0.00143 gramme, 
or 1.2 per cent, and consisting of minute black specks with a fused ap- 
pearance. The iron of this ash, as determined by titration with a weak 
* Arch. f. exp. Path. u. Pharmakol., Bd. xxvi, p. 139. John J. Abel and Walter S. Davis 
35 
solution of permanganate, amounted to 0.00016 gramme, or 0.14 per 
cent of the amount of pigment taken. 
The ash of the hair pigment was also analyzed as above described, 
and with similar results. When purified until a low ash content was 
obtained—say 2.19 per cent—the iron was also found to amount to far 
less than 0.1 per cent. Thus, 0.4492 gramme of substance gave 0.0078 
gramme of ash, the iron of which, as determined by titration with weak 
permanganate, amounted to 0.00026 gramme, or 0.057 per cent. 
The iron determinations recorded in this paper, both of the gran- 
ules and of the pigment, were made in three ways, and we have usu- 
ally indicated in each case which method was employed. When only 
a mere trace of iron was thought to be present, the method of analysis 
was by colour titrations with potassium sulphocyanide; the second 
method, the one most frequently employed, was by titration with a 
solution of potassium permanganate, each cubic centimetre of which 
was capable of oxidizing 0.00043 gramme of iron; the third was by 
the gravimetric method of Ludwig and Gottlieb, which has been found 
trustworthy up to the limit of half a milligramme of iron, when 
only small filters and small quantities of reagents are used. Thus, one 
of us (Abel) recovered by this method half a milligramme of iron 
from a few cubic centimetres of a solution containing precisely that 
amount of iron which had been standardized by Dr. T. B. Aldrich. 
Miss Katharine Porter also recovered by this method 0.00239 gramme 
of Fe203 out of 0.00244 gramme taken. The re2o3 was prepared 
from pure ferric chloride. 
16. The Origin oe the Pigmentary Substance. 
When a pigment is found to contain iron, this fact has been 
thought to furnish some evidence that it is a derivative of hemo- 
globin; but if no iron is present, it may still claim that source, for 
the animal organism contains a number of pigmentary substances, 
such as hematoidin and bilirubin, that have no iron'in their com- 
position, and which, nevertheless, are derived from hemoglobin. This 
class of iron-free pigments, it will be remembered, lack the element 
sulphur. 36 
On the Pigment of the Negro's Shin and Hair 
The coloured substances of the epidermis and hair agree with this 
class in containing no iron, but they differ in that they contain a con- 
siderable amount of sulphur, which we must consider to be present as a 
constituent part of their molecule. We are not at present acquainted 
with any coloured natural derivative of haemoglobin that contains 
sulphur, nor do we know of any such produced by chemical means. 
The proteid moiety of haemoglobin contains but little more than a 
half per cent of sulphur, while our pigment contains at least three 
times this amount. 
The presence of sulphur in the pigment makes it certain that it 
is derived from a proteid, and we can as easily suppose some proteid 
of the blood to be the direct precursor of the pigment as that haemo- 
globin should be decomposed in order that its proteid moiety may 
serve this purpose. We should have an equal right to assert that 
keratin is derived from haemoglobin. 
17. Total Amount of Pigment and of Pigmentary Granules 
in the Skin of One Negro. 
The entire skin, with the exception of that on the palms of the 
hands and soles of the feet, was removed from the cadaver of a tall, 
slender negro, and from this skin the epidermis was removed with 
the exception of a few small areas. After being cleansed with water, 
alcohol, and ether, the epidermis thus obtained was found to weigh 
34.08 grammes. Making a liberal allowance for the thicker epidermis 
left on the feet and hands, and the small areas not removed from the 
knees and elbows, we may assume that the entire removable epidermis 
of the negro in question, when freed of hairs, fatty substances, water, 
etc., would have weighed 40 grammes. 9.9306 grammes of this epi- 
dermis yielded 0.2182 gramme of pigment, the pigment being gath- 
ered and weighed immediately after its first precipitation. Calcu- 
lated on this basis, we find that the epidermis of this cadaver must 
have contained at least 0.8789 gramme of pigment. The individual 
in question was judged to be a full-blooded negro, but his colour was 
of the bronzed order rather than deep black. The epidermis was also 
thinner than usually seen, and the case may therefore be assumed to John J. Abel and Walter S. Davis 
contain somewhat less than the average amount of pigment. We 
therefore assume the average amount of the pigmentary substance, 
as at present isolated, to be in the neighbourhood of 1 gramme for 
an adult negro of average body surface. If we assume, also, that the 
pigmentary granules as lodged in the living cell contain sixty-five per 
cent of water and about five per cent of mineral constituents, there 
would be found in the skin of the average negro about 3.3 grammes 
of pigmentary granules. 
18. Function of the Epidermal Pigment. 
While we ourselves have done no work on the function of the 
pigment, the subject is one of such interest that we must be allowed 
a brief account of the investigations of others. 
Horn * exposed his own hand alongside of that of a negro to the 
direct rays of the sun, with the result that his own hand became in- 
flamed, while that of the negro remained unaffected, thus showing 
how great a protection is afforded by the pigment of the negro’s skin. 
0. Eijkmann,f of Batavia, has recently published a most interesting 
experimental research on the regulation of body temperature among 
whites and Malays in Batavia. The relative ability of the two kinds 
of skin to radiate and conduct heat, and the extent to which sweating 
takes place in the two races, were carefully studied. By the follow- 
ing experiment the two kinds of skin were also compared as to their 
ability to absorb sunlight, in which respect they were found to differ 
markedly. Two thermometers exactly alike were treated as follows: 
The bulb of one was covered, first, with a piece of skin from a Malay, 
and outside this with a piece of skin from a white man. On the second 
thermometer the order of the skin wrappings was reversed, the white 
skin being put next the bulb and the brown skin outside. After a 
period of exposure in a moist chamber to the direct rays of the sun, 
* Cited from Boubnoif, Ueber das Permeabilitatsverhaltniss der Kleidungs- 
stoffe zum chemisch wirkenden Sonnenstrahl. Arch. f. Hyy., Bd. x, p. 363. 
This investigator’s name is given as Horn by Eijkmann in Virchow’s ArcJiiv, 
Bd. cxl, p. 157. 
t Virchow’s ArcMv, Bd. cxl, p. 125. 38 
On the Pigment of the Negro's Skin and Hair 
the first thermometer registered 47.5° C., the second 50.1° C. Eijk- 
mann also says that the brown skin felt distinctly warmer to the hand 
than the white skin. Now Widmark * has shown that the ultra-violet 
rays of the spectrum are far more effective in causing that superficial 
inflammation known as sunburn (erythema solare) than are the rays 
of less rapid undulation. Indeed, sunburn and that more marked 
inflammation resulting from exposure to a very powerful electric arc 
light are both caused to so preponderating an extent by the ultra- 
violet rays that heat, the degree of illumination, and other factors that 
have hitherto been regarded as causative agents, may be entirely 
neglected. 
Hammer f has furnished corroborative experiments by covering 
the skin with ointments and lotions containing sulphate of quinine, 
which has the power of changing violet rays and ultra-violet rays to 
less refrangible ones, and has thus succeeded in greatly lessening the 
inflammatory action of sunlight and of the arc lamp. Bouchard is 
also cited by Paul Bert $ as having demonstrated that violet rays are 
more effective in raising a blister than rays of less refrangibility. 
Hammer has also abstracted from the literature of dermatology a 
number of interesting cases of great sensitiveness of the skin to light, 
and in all of these cases it was shown that the chemically active rays 
alone were responsible for the inflamed condition of the skin. 
It is a matter of common observation that the photograph of a 
negro is indistinct and unsatisfactory compared with that of a white 
man, the light reflected from the black skin having been largely de- 
prived of its actinic quality. Boubnoff’s # experiment with frog’s skin 
placed over sensitive plates has also shown how effective are thor- 
oughly pigmented areas in absorbing the chemically active rays of 
light. It may therefore be assumed that it is one function of the 
pigment to absorb the chemical energy of the sun’s rays, and, although 
the pigmentary layer of the skin would thereby tend to take on a higher 
* Cited at length in Hammer. Ueber d. Einfiuss des Lichtes auf d. Haut. 
t Op. cit., pp. 33-41. 
Stuttgart, 1891, pp. 39-33. 
t Rev. scientifique, 1878, No. 42, p. 987. 
# Log. cit., p. 362. John J. Abel and Walter S. Davis 
39 
temperature, yet the inflammation of the more sensitive vascular corium 
underneath is in reality prevented. 
19. Conclusions. 
The pigmentary granules of the negro’s skin and hair can be 
freed in several ways from the cells in which they are lodged and 
collected in any desired amount. 
As thus obtained, these granules are found to be insoluble in dilute 
alkalies, dilute hydrochloric acid (hot or cold), alcohol, or other organic 
solvents when applied in the order named. If, after they have been 
subjected to the action of dilute hydrochloric acid, they are again 
treated with dilute alkalies, they are found to give up their pigment, 
and, on the continued application of heat, the granules dissolve en- 
tirely in the alkaline solution, leaving only an insignificant residue. 
The pigmentary granules are composed of a colourless ground 
substance or substratum, a pigment, and much inorganic matter. 
Their inorganic constituents, as thus far determined, are calcium, 
magnesium, iron, and silicic, phosphoric, and sulphuric acids; and 
these constituents possibly play an important part in the deposition 
and fixation of the colouring matter in the granules. 
The pigment isolated from the granules, and sufficiently freed 
from adherent inorganic matter, contains only the merest trace of 
iron—so little, in fact, that we must think of it when entirely pure as 
free of iron. Heating the isolated pigment with barium hydrate at 
a temperature of 260° C. entirely frees it from the closely adherent 
ground substance, and it is then found that the vapours of pyrrol are 
no longer emitted when it is subjected to dry distillation, and the 
odour of burnt feathers is no longer discerned, although nitrogen 
is still present. 
We can not conclude as the result of our work that the pigment 
is a derivative of haemoglobin; it seems to us more probable that it 
is ultimately derived from the proteids of the parenchymatous juices. 
The total quantity of soluble pigment in the skin of a negro of aver- 
age size is found to weigh about 1 gramme; the weight of the pigmen- 
tary granules is about 3,3 grammes, if we are right in our assumption 40 
On the Pigment of the Negro's Shin and Hair 
that they contain sixty-five per cent of water and five per cent of min- 
eral constituents in their natural state in the epidermis. 
The pigments of the epidermis and hair of the negro are very 
likely identical. In the present state of our knowledge we can only 
say that it seems highly probable that the pigment of the negro’s hair 
is not different from the dark pigment found in the hair of the white 
races, and we may infer that the pigment of the black skin differs only 
in amount and not in kind from that deposited in the skin of the 
white man. 
Description oe Plate XIY, 
Fig1. 1.—A single cell from the lowest stratum of the rete mueosum, show- 
ing the pigmentary granules. 
Fig. 2.—The epidermis after maceration for two hours and a half with a 
five-per-cent solution of potassium hydrate. 
Fig. 3.—The same after maceration for six hours. The pigmentary 
granules here seen have been spread out in a thin layer by slight pressure 
on the cover glass. 
Fig. 4.—The dried pigmentary granules in the form of the snuff-coloured 
powder described in the text, mounted in water. 
Fig. s.—The pigmentary granules of the epidermis stained with Ehrlich’s 
gentian-violet solution after having been boiled in a sealed tube with a mix- 
ture of concentrated ammonia and alcohol. 
Fig. 6.—A piece of hair macerated for fifteen minutes in five-per-cent 
potassium hydrate and then crushed and mounted. It shows the large 
ovoidal pigmentary granules. 
Fig. 7.—The isolated pigmentary granules of the hair stained with Ehr- 
lich’s gentian-violet solution, after having been partially decolourized by 
means of concentrated ammonia and alcohol. THE JOURNAL OF EXPERIMENTAL MEDICINE. VOL. I. 
PLATE XIV, 
FIG. I. 
FIG. 2. 
FIG. 3. 
FIG. 4. 
FIG. 7. 
FIG. 6. 
1000 
I