Extracted from the 
TRANS ACTIONS OF THE COLLEGE OF PHYSICIANS OF 
PHILADELPHIA. 
THIRD SERIES, VOLUME III. ON THE 
» 
INTERNAL ADMINISTRATION OF NITRATE OF 
SILVER, AND ON THE OCCURRENCE OF A 
BLUE LINE UPON THE GUMS AS THE 
EARLIEST SIGN OF ARGYRIA. 
By 
WILLIAM PEPPER, A.M., M.D., 
PROFESSOR OF CLINICAL MEDICINE IN THE UNIVERSITY OF PENNSYLVANIA. 
[Read March 7, 1877.] 
It is of coarse not within the province of the' 
present article to discuss the very numerous and 
varied conditions in which the internal administration 
of nitrate of silver is strongly indicated. Suffice it to 
say that there are few remedial agents whose thera- 
peutic value and range of application are equally ex- 
tensive. This is not surprising when it is remembered 
that nitrate of silver possesses a peculiarly valuable 
local action in addition to its power of directly affect- 
ing the nervous system by absorption. The topical 
action of nitrate of silver, given internally, even in 
small doses, may be said to extend throughout the 
entire gastro-intestinal tract, with, perhaps, the excep- 
tion of the rectum. In addition to this, it appears to 
me to be established by clinical evidence that a certain 
amount of influence is produced on the continuation 
of the duodenal mucous membrane into the common 
hepatic duct, and possibly into the pancreatic duct. 
This local action is in part that of an astringent, but 40 
PEPPER, 
in addition it presents a peculiar, alterative character. 
Its power of influencing nutrition enables the nitrate 
of silyer to modify the morbid action of ulcers of the 
stomach or intestinal canal, and to cause the reduction 
of chronic inflammatory thickenings of the mucous 
membrane, and of hypertrophies of its glandular appa- 
ratus. Associated with this is its power of allaying 
morbid irritability of the nerves of the mucous mem- 
brane, and of influencing the secretions. 
The exact form which nitrate of silver assumes after 
entering the stomach is not known, and probably is 
not the same in all cases. It is.evident, however, that 
it cannot long retain its integrity. Probably it is 
sometimes converted into a chloride, though more 
frequently it would seem to unite with the albuminous 
peptones, forming a compound which does not coagu- 
late albumen, and which is readily dissolved in albu- 
minous liquids. In this form it may easily be under- 
stood how, even when given in minute doses, if 
frequently repeated and continued for a considerable 
time, it may produce a powerful action throughout 
the entire extent of the mucous tract before mentioned. 
Among the special morbid conditions for which it 
has been recommended, on account of its local action, 
I would especially mention the following, based upon 
my own personal experience: in the stomach—gastric 
ulcer, chronic catarrhal gastritis, especially with fre- 
quent vomiting or with pain dependent upon morbid 
irritability of the nerves of the mucous membrane; in 
the intestinal canal—cases of follicular (catarrhal) 
enteritis, both in the adult and in the child, subacute 
and chronic dysentery, chronic typhlitis, and tubercu- 
lous diarrhoea. I have also lately obtained remarkable INTERNAL USE OF NITRATE OF SILVER. 
41 
results from the administration of nitrate of silver in 
eases of gastro-hepatic catarrh, with or without jaun- 
dice from occlusion of the ducts by tumefaction of the 
mucous membrane. Recent observation has, more- 
over, led me to believe that the administration of this 
drug in typhoid fever, as originally recommended by 
Boudin in 1836, is a very valuable element of treat- 
ment in this important affection. In addition to all of 
these must be mentioned the great value of injections 
of nitrate of silver in many forms of rectal disease. 
With regard to its absorption and effects upon the 
general system, the evidence is no less satisfactory. 
The fact of its absorption does not indeed admit of 
doubt. Apart from the positive therapeutic effects 
observed, there is the actual proof of the detection 
of silver in various internal organs, and of its deposit 
in the skin after its long-continued administration. 
Given thus internally, the chief action of the salt 
would seem to be upon the nervous centres, whose 
nutrition it possesses the power of modifying to a con- 
siderable degree, though the precise mode in which 
this is accomplished is still uncertain. The diseases 
for which nitrate of silver is used in view of its con- 
stitutional effects are chiefly affections of the nervous 
system, such as epilepsy, chronic meningitis, and 
sclerosis of the spinal cord. 
In regard to a remedy of such value and wide appli- 
cation, it is important to consider what difficulties 
attend its administration, and how they may best be 
overcome. The first difficulty which suggests itself 
is connected with the local irritant action which nitrate 
of silver occasionally produces. This, however, can 
always be avoided by giving the remedy in pill form, 42 
PEPPER, 
and by graduating the dose carefully in accordance 
with the sensibility of the stomach. Thus, my own 
rule is to begin the administration of this drug in 
doses of from one-sixtli to one-fourtli of a grain three 
times a day, to give it in pilular form, and soon after a 
little light food has been taken. If necessary, its irri- 
tant action may be still further guarded against by 
combining with it a small quantity of opium. 
It is usually stated that when the local action on the 
alimentary canal is desired, the drug should be given 
one or two hours before meals, on an empty stomach; 
while when the constitutional effect is desired, the pill 
should be given after meals, during the process of 
digestion. In most cases where nitrate of silver is 
given for its local action, it is necessary to employ 
a diet carefully restricted, both as to quantity and 
character; and it has seemed to me that the good 
effects of the remedy are not interfered with by its 
being administered half an hour to an hour after a 
very light meal, especially of a fluid character, such as 
skimmed milk or broth. It is certain that the danger 
of causing gastric irritation is much lessened when this 
drug is thus given, instead of being given on an empty 
stomach before meals. In cases where the diet allowed 
is not so rigidly restricted, and considerable quantities 
of food are taken at each meal, and yet the adminis- 
tration of the silver on an empty stomach causes irrita- 
tion, I have found it useful to give a few spoonfuls of 
light arrow-root a couple of hours before the regular 
meal, and to administer the silver immediately after 
this. 
The second great difficulty attaching to the internal 
administration of nitrate of silver is the tendency to INTERNAL USE OF NITRATE OF SILVER. 
43 
discoloration of the skin by the deposit of the silver in 
its tissues. This discoloration of the skin has long 
been known. Fourcroy (Medecine eclairte par les 
Sciences Physiques, tome i. p. 342) was among the 
first to call attention to it; Dr. I. A. Albers, of Bre- 
men, communicated a case to the Royal Medico-Clii- 
rurgical Society of London, in 1815 (Med.-Cliir. 
Transactions, vol. vii. p. 284); and sin6e that time 
numerous cases have been placed upon record. 
The skin first presents a peculiar, bluish-slate color 
which may deepen until the patient acquires a hue of 
the deepest lividity. In some cases, where the dis- 
coloration has become very intense, the color is 
described as bronzed. This discoloration is usually 
said to he deepest in parts exposed to the light, as the 
face and hands. The whole surface is, however, 
involved, and in severe cases the sclerotic coats of the 
eyes, the mucous membrane of the mouth, and even 
the internal organs, as the liver, spleen, and kidneys, 
have been found to he discolored. So grave is the 
danger of inducing this condition, and so universally 
is it regarded as a serious contra-indication to the use 
of this valuable remedy, that it is important to con- 
sider somewhat more in detail (1) the cause of this 
discoloration; (2) the shortest period of administra- 
tion and the smallest quantity of the nitrate of silver 
after which it has been known to occur, and (3) the 
best mode of avoiding this unfortunate result. 
In regard to the first of these points, the fact that 
the discoloration is not limited to the external surface, 
hut affects also the internal organs, goes far to prove 
that it is not due to the chloride of silver, hut to a 44 
PEPPER, 
deposit of the metal itself or its oxide, and this view 
is further confirmed by chemical examination. 
The amount of silver in the tissues required to pro- 
duce this discoloration is extremely small, thus H. C. 
Wood quotes the analysis of the organs in a case of 
Versmanns (Virchow’s Arcliiv, xvii., 1859), who in 
14.1 grammes of dried liver found only 0.068 gramme 
of metallic silver (0.047 per cent.), and in 8.6 grammes 
of dried kidney, 0.053 gramme (0.061 per cent.). 
The smallest amount which has ever been known 
to produce general discoloration is difficult to deter- 
mine. It has been known to follow the use of one 
hundred and twenty grains, given in the dose of half 
a grain daily for eight months consecutively; while 
again, in a case reported by Bertini (De usu interno 
preparationum argenti, Thesis inauguralis. Geneva, 
1814), thirty-three and a half drachms Avere taken in 
a period of two years and a half, averaging two and a 
half grains daily. These cases may perhaps be taken 
as representing about the extremes ; but in the latter 
instance it is not stated how long the drug had been 
taken before the discoloration was first noticed, nor is 
it possible, of course, to form any idea of how much 
of the great amount given passed through the alimen- 
tary canal unabsorbed. 
With regard to the length of time necessary for the 
development of the discoloration, Dr. James Johnson 
asserts that there is no case of discoloration on record 
in which the use of the medicine had not been con- 
tinued beyond three months. Much more frequently, 
however, When argyria, or discoloration of the skin 
by silver, is produced, it will be found that the patient 
has continued the use of the remedy with or without INTERNAL USE OF NITRATE OF SILVER. 
45 
the advice of the physician for a ranch longer period 
of time than the above, usually eighteen months or 
over. It is interesting to note, in this connection, 
that so large a proportion of the recorded cases of 
argyria has occurred in epileptics. It is well known 
that, before the discovery of the peculiar powers of 
the bromides, the long-continued use of large doses 
of nitrate of silver was strongly recommended in this 
disease. 
Another peculiarity connected with argyria, accord- 
ing to some observers, is that the discoloration con- 
tinues to deepen for some time after the use of the 
remedy has been suspended. It is even asserted 
(Sigmund, Lancet, March 31, 1838) that in some in- 
stances the discoloration does not occur until some 
months after the remedy has been discontinued, but 
this appears to me very improbable, and certainly 
needs confirmation. 
In regard to the mode of avoiding this unfortunate 
result, various suggestions have been made. Thomp- 
son proposed the simultaneous administration of nitric 
acid, with a view of preventing the conversion of the 
nitrate into the chloride. This, however, has been 
shown, both theoretically and practically, to be useless. 
The majority of authors content themselves with re- 
commending that the administration of the silver salt 
should be suspended after a period which, according to 
different authorities, varies from three weeks to three 
months. It is evident, however, that this is altogether 
too vague to be depended upon. It would be more 
valuable could some safe limit as to the quantity to be 
used be determined. My own rule, for a number of 
years, has been to continue its administration in doses 46 
PEPPER, 
of from one-fifth to one-third of a grain thrice daily until 
thirty grains have been taken; to then suspend it for 
one month; after that interval to resume and continue 
its administration until fifteen grains more have been 
taken; and again to withdraw it either permanently 
or for another month, to be then followed by a final 
course of fifteen grains, making sixty grains in all. 
One great defect, however, of such rules, is that they 
only fix a minimum dose without reference to the 
individual features of the case, and, of course, without 
any accurate knowledge of the proportion of the 
remedy absorbed in different instances. Thus, among 
other considerations which deserve attention, is the 
weight of the patient. In the case of nitrate of silver, 
as of many other drugs capable of producing an effect 
on the whole body, it cannot be doubted that one of 
the factors, in determining the amount that can be 
tolerated in any given case, is the weight of the sub- 
ject. But when we consider the extreme value of 
this remedy in certain conditions, it becomes evident 
that what we need, is a rule which will enable us to 
administer, in any given case, the maximum dose 
consistent with entire safety. It is with the hope 
of establishing such a rule that I venture to bring 
forward the results of certain recent observations that 
I have made, which go to show that the earliest sign 
of argyria, occurring before there is any danger of the 
slightest discoloration of the shin, is a 'peculiar blue 
line on the gums. 
The following cases are given in illustration of this 
position. It may be premised that crystals of nitrate 
of silver were used exclusively in compounding the INTERNAL USE OF NITRATE OF SILVER. 
47 
pills.administered in these cases, and that consequently 
there is no chance of any lead having been admixed. 
This is mentioned because the nitrate of lead is some- 
times associated with the nitrate of silver in the form 
of stick. 
Case I. Chronic Gastro-hepatic Catarrh.—Mrs. W., pet. 60, 
of unusually large frame; had suffered from deep jaundice of 
six months’ standing, subject to marked variations in inten- 
sity, and associated with frequent spells of hepatic colic from 
closure of the common duct owing to swelling of the mucous 
membrane. Treated by nitrate of silver and Carlsbad water, 
with restricted diet. Complete cure at end of eight months. 
About sixty grains of nitrate of silver were given in all, in 
doses of one-sixth to one-fourth of a grain three times a day 
in pill form. Thirty grains were given at first, then, after an 
interval of a month, fifteen grains more; and later, after a 
longer interval, fifteen grains more. ISTo trace of discolora- 
tion of the skin, and no line on the gums. 
Case II. Chronic Gastro-hepatic Catarrh.—Mrs. G., set. 58, 
of medium size, was desperately ill for many months, with 
deep jaundice, clay-colored stools, irregular chills and fever, 
frequent vomiting, extreme emaciation, intense attacks of 
hepatic colic: no gall-stone. Complete cure resulted from 
the use of nitrate of silver, given in doses of one-fourth of 
a grain with a small dose of opium three times a day. About 
fifty grains were given. At the close of this time a blue 
line made its appearance on the lower gum corresponding to 
the twro incisors, canine, and first premolar teeth on right 
side of jaw. The line was close to junction with teeth, and 
closely resembled the lead line. The nitrate of silver was 
dispensed in form of crystals. 
Case III. Gastric Ulcers.—Mrs. B., set. 30, rather small- 
sized, slender woman. Gastric ulcer, profuse hemorrhage, 
intense gastralgia and heartburn. After controlling the 
hemorrhage, nitrate of silver was given in pill form, in doses 
of one-fourth of a grain, thrice daily, taken immediately after 48 
PEPPER, 
taking small quantities of milk. Rapid improvement. About 
forty-five grains of nitrate of silver were taken in all, ex- 
tending over a period of about two months. One month 
afterwards, examination of her mouth showed a very marked 
blue line on lower gum, corresponding to the five or six 
teeth to the right of the median line. The nitrate of silver 
was given in the form of crystals. 
Case IV. Chronic Perityphlitis.—II. W., set. 25, suffering 
with chronic perityphlitis from a strain; seen in consultation 
with Dr. Santee; was treated with restricted diet and nitrate 
of silver in pill form. About fifty grains in all were taken 
between July 5, 1876, and October 1,1876. After the above 
period it was discovered that there was a very marked blue 
line on the gums, closely resembling the blue line of lead- 
poisoning.1 This chiefly affected the lower jaw, where it 
corresponded to about six or seven teeth counting to the 
right from the left lateral incisor. 
The line was quite broad, in places nearly one line. On 
the upper jaw a slightly developed line was noticed, corre- 
sponding to the right lateral incisor, canine, and first, premo- 
lar. In addition to this, there was some excessive pigmenta- 
tion of the mucous membrane of the lower lip near its junction 
with the gum. There was no trace of discoloration of the skin. 
A small piece of the discolored portion of the gum was cut 
out and placed in the hands of Dr. E. 0. Shakespeare, who 
has kindly furnished the following report of the microscopi- 
cal and micro-chemical examination of the specimen :—• 
The small portion of tissue from the gum was hardened 
in dilute alcohol, and, when of sufficient consistence for 
cutting, the piece measured in length A inch, in breadth A 
inch,and in thickness Tin inch. It was imbedded in paraffin 
in order to make thin sections from it. Cuts were intended 
to be made vertical to the upper edge of the gum and to its 
anterior epithelial surface, but, when placed under the mi- 
! The painting, which was exhibited in connection with this case, has not 
been reproduced, on account of this close resemblance between the silver 
line and the familiar blue lead line on the gums. INTERNAL USE OF NITRATE OF SILVER. 
49 
croscope, they were found to he somewhat oblique to the 
latter surface. Some of these sections were stained with 
carmine and mounted in balsam, others were mounted in the 
same medium unstained. The accompanying drawing, by 
Dr. Shakespeare, represents one of the former, enlarged one 
hundred and fifty diameters. (See wood-cut.) 
Section of gum, showing supposed silver deposit along course of vessels.— 
a. Auterior epithelial surface, b. Upper edge of gum. c. Corneous layer 
of epithelium, d. Rete mucosum. e. Layer of cylindrical cells. /. Fibrous 
substance of gum. g. A few black granules deposited along vessels of 
papillae, h. Dark granular deposit covering and occupying the vessel walls. 
Under the' microscope, the stained section exhibited the 
following appearances : The epithelial layer of the gum was 
a little thickened. The layer of cylindrical cells covering 
the papillary surface was so entirely free from pigment as to 
lead to the assumption that the patient was very light-com- 
plexioned. The outlines of these palisade-like cells were 
slightly indistinct, the contents finely granular, and the. 
nuclei large and deeply stained. The cells of the rete Mal- 
pighii presented large, deeply stained nuclei, granular contents 
and ill defined outlines. The squamous epithelium near the 
corneous layer, which was not increased much in thickness, 
also showed nuclei very distinct and well stained. Through- 50 
PEPPEK, 
out the sub-epithelial, dense, fibrous tissue of the gum, as well 
in the papillae as in the deeper portions, but particularly in 
the latter, was to be observed a very considerable and diffuse 
cellular infiltration. This cellular infiltration has not been 
represented in the drawing, but in other respects the IStter 
is as nearly as possible an accurate copy of the microscopic 
picture presented by the section from which it was made by 
aid of the camera. In the deeper portion of the fibrous 
tissue of the gum, and not much below the superior edge, a 
dark granular deposit was very distinctly seen to occupy the 
position of the large veinules and capillaries, which here 
mainly pursue a course parallel to the anterior epithelial 
surface. Under Hartnack’s BTo. 11, 4, Immersion, no crystal- 
line forms could be detected in the deposit, nor could it be 
discovered that the granular particles wTere contained within 
the bodies of cells of the surrounding cell infiltration. In 
one or two of the papillae, scarcely visible traces of these dark 
granules could be made out at points along the capillary loop. 
The granules forming the above deposits were variable in 
size and color, the latter ranging from dark brown to black 
by transmitted light, and the former not differing from that 
of the granules often found in silver staining. They were 
sufficiently numerous to mask the vessel wTall where they 
occurred. 
The next point to be determined was, whether this dark 
granular deposit so distinctly limited to the course of the 
deeper vessels of the gum, was some form of the blood pig- 
ment, or was silver in some shape. Of the coloring matters 
of the blood, hsematin and melanin are granular and dark- 
brown or black. The others are crystalline, and may be ex- 
cluded from further notice here. Hsematin is soluble in 
either an aqueous or a spirituous solution of ammonia. Mela- 
nin is not at all or only slightly soluble in a strong solution 
of cyanide of potassium. Oxidized silver is readily soluble 
in the latter solution. In order to distinguish between these 
three substances, the following tests were applied to several 
sections of the small portion of gum:— INTERNAL USE OF NITRATE OF SILVER. 
51 
Several sections, in which could be well seen the dark, pre- 
viously described deposit, were macerated for a considerable 
time in an aqueous solution of ammonia, rather strong. 
Upon subsequent examination under the microscope, the 
deposit appeared not to have decreased in density or to have 
changed at all. Other sections were macerated a few moments 
in a strong solution of cyanide of potassium, and were sub- 
sequently placed in the field of the microscope. From these 
sections every trace of the granular deposit had vanished. 
A fresh piece of the choroid coat of the human eye, after 
staining with silver, and exposure to light, was placed in 
an equally strong solution of cj’anide of potassium, and the 
effect was observed under the microscope. The black silver 
lines rapidly disappeared, but the pigment in the hexagonal 
cells and in the stellate cells of the stroma of the choroid 
remained untouched. One other micro-chemical test was 
applied. Either the chromate or the bichromate of potassium 
gives, with nitrate of silver, a precipitate which is red by 
reflected light. Several sections showing clearly the granular 
deposit, were macerated a moment in a drop of nitric acid, 
rather strong. The nitric acid was then removed, and the 
sections were covered with a drop of a solution of bichromate 
of potassium, in which they were permitted to remain a few 
moments. They were subsequently well washed and mounted 
in glycerine. Viewed by reflected light, and under a low mag- 
nifying power, the formerly dark deposit now gave a distinctly 
red reflex when seen in sunlight. The bichromate had, as 
usual, stained the mass of the tissue yellow, and this color 
had the effect of slightly modifying the red so as to produce 
a yellowish-scarlet or an orange tinge of red. Microscopic 
examination by reflected light, of the previously-mentioned 
unstained section mounted in balsam, showed a whitish or 
grayish reflex from the position of the deposit, which, by 
transmitted light, appeared dark and granular. From the 
preceding examination I am, therefore, inclined to think that 
it is highljr probable that the mass of the dark granular 
deposit above alluded to, consists neither of hsematin nor of 
melanin, but that it is composed of silver. 52 
PEPPER, 
At the time the above cases were examined, as I 
had never happened to see any allusion to such early 
staining of the gums in advance of general argyria, 
I fancied that the observation was an original one. 
On coming to examine the literature of the subject, 
however, I soon found that this was far from being 
the case. Dr. George B. Wood states (Treatise on 
Therapeutics, etc., 2d ed., 1860, vol. i. p. 401), “ hap- 
pily, before the skin begins to exhibit this hue, a 
similar dark discoloration usually appears upon the 
gums and tongue and in the fauces, and serves, if 
observed, to put the practitioner upon his guard.” 
This statement appears to rest upon the authority of 
the original observer since, in the United States Dis- 
pensatory (thirteenth edition, 1870, p. 1049), Dr. IVood 
states again, “ according to Dr. Branson, an indica- 
tion of the approach of discoloration is furnished by 
the occurrence of a dark blue line on the edges of the 
gums, very similar to that produced by lead, but some- 
what darker.” I have been unable to find Dr. Bran- 
son’s communication on this subject, nor do I find 
that his observation attracted lasting attention, since, 
with the two exceptions above given, I have not 
covered any allusion to this important phenomenon 
occurring as a premonitory sign of argyria, in any of 
the numerous recent works on Therapeutics which I 
have consulted. I am glad, therefore, to have been 
led, by observing anew this blue silver line on the 
gums, to call attention to Dr. Branson’s original 
observation. The practical importance of this sign 
is considerable. I believe that it enables us to admin- 
ister nitrate of silver internally with safety so far as 
any danger of discoloration of the skin is concerned, INTERNAL USE OF NITRATE OF SILVER. 
53 
provided that the gums be examined every few days, 
and that the use of the remedy be suspended as soon 
as the characteristic blue line is observed. 
Another point of importance is its close resem- 
blance to Burton’s blue line on the gums, due to the 
saturation of the system with lead. Indeed, in some 
of the cases I have recorded, it would have been im- 
possible to determine, by inspection alone, whether 
the blue line was due to lead or not. It may be said, 
however, that in other instances the color of the silver 
line is darker and more decidedly blue, and also that 
there is a tendency for the discoloration to extend 
to a greater distance on to the gum from the line of 
junction with the teeth, and also for it to affect the 
mucous membrane of the lips near the junction with 
the gums. It will hereafter be necessary, however, in 
any case where a blue line is observed on the gums, 
to investigate the history of the case not only with 
regard to the action of lead, but also of silver. 
The safeguard which I have above proposed, and 
which, I trust, will prove to be a constant and reliable 
phenomenon, becomes of greater importance when it 
is borne in mind that the discoloration of the surface 
is, as a rule, permanent. I have known several cases 
where it continued unchanged after the lapse of 
twenty years, and similar instances are not scarce in 
medical records. It is true that Orfila (Medical Times 
and Gazette, March, 1852, p. 279) found silver in the 
liver of animals, to which the nitrate had been given, 
six months after its administration; but found that in 
seven months it had disappeared from the tissues of 
animals similarly treated. And so, in certain cases, 
argyria has been stated to gradually diminish with 54 
PEPPER, INTERNAL USE OF NITRATE OF SILVER. 
the progress of time. So, too, success has been 
claimed for various remedies in the treatment of 
argyria. Thus repeated blistering, alkaline baths, the 
prolonged use of cream of tartar and iodide of potas- 
sium, have all been recommended. Of these, iodide of 
potassium has most evidence in its favor, and is the 
one on which I should myself rely; but still in several 
instances it has been vigorously employed without 
success. 
After the discontinuance of nitrate of silver in 
Case TV., iodide of potassium was directed with a view 
of favoring the absorption of the indurated cellular 
tissue surrounding the caecum. This has given the 
opportunity of observing the influence of time, in con- 
nection with the use of the iodide, upon the blue line 
on the gums. At the present time, six months after 
discontinuance of the nitrate of silver, the line has 
perceptibly, though slightly, faded in intensity. 
It is very possible that the difference in the persist- 
ence of the argyria, and in the results of treatment 
in different cases, may depend somewhat upon the 
amount of silver which has been absorbed and fixed 
in the tissues.