Reprinted from the American Journai of Physiology. 
Vol. 111. December i, 1899. No. V. 
A NEW FORM OF PISTON RECORDER AND SOME OF 
THE CHANGES OF THE VOLUME OF THE FINGER 
WHICH IT RECORDS. 
WARRIj N P. LOMBARD and W. B. PILLSBURY. 
[From the Physiological Laboratory of the University of Michigan.] A NEW FORM OF PISTON RECORDER AND SOME 
OF THE CHANGES OF THE VOLUME OF THE 
FINGER WHICH IT RECORDS. 
WARREN P. LOMBARD and W. B. PILLSBURY. 
[.From the Physiological Laboratory of the University of M 
OF the many forms of apparatus which have been devised for re- 
cording small changes in volume of members or organs of the 
animal body, the most delicate is Ellis’s piston recorder.1 This 
instrument gave good results in the hands of its ingenious inventor, 
but was so fragile that it has never come into general use. It con- 
sisted of a glass tube, containing a piston of paraffin connected by a 
straw piston rod with a lever of straw and paper. The piston was 
turned almost to fit the tube, the intervening space being filled with 
a volatile oil, such as oil of peppermint or cloves. The fact that the 
oil tended to dissolve the paraffin was considered an advantage, as 
it caused a more complete union between them and helped to secure 
an air-tight closure of the tube. Ellis chose air in preference to 
water or oil as a medium for transmitting the changes in volume; 
in part, because air is not liable to the oscillations which are seen 
in a column of liquid when suddenly moved, and, in part, because 
air can be employed without subjecting the organ to be studied 
to external changes in pressure. Since air is easily compressed, it 
was necessary that his recording apparatus should offer the least 
possible resistance to the movement of the air; he therefore con- 
structed it ol the lightest materials, and sought to avoid every form 
of friction. 
Several investigators 2 have described more or less modified forms 
of Ellis’s instrument, and Hurthle,3 in his excellent article on trans- 
mission of pressures by air, recounts a series of experiments made to 
ascertain the best form of piston recorder, and its efficiency as com- 
pared with the recording tambour. The form which he found to give 
1 Ellis, F. W. : Journal of physiology, 1886, yii, p. 309. 
2 Johansson and Tigerstedt : Skandinavisches Archiv flir Physiologic, 1889, 
'1 P- 345 j Schafer, E. A. ; Journal of physioloo'v, 1884, v. p. 130. I— 
-3 Hurthle: Archiv f. d. ges. Physiol., 1893, lliifp. 30?. ' i - \ > ' \ A New Form of Piston Recorder. 
187 
the most accurate results, and which he states to be the best instru- 
ment thus far devised for recording air waves, was considerably 
lighter than that used by Johansson and Tigerstedt, the total weight 
of the movable parts being only 0.68 gram. Although heavier than 
the form employed by Ellis, it had the advantage of durability. 
The writers of this paper, having become interested in a line of 
work which required an accurate record of very slight changes in 
volume, found it necessary to employ Ellis’s method, and to give 
to his instrument a more permanent form. Not being at the time 
aware of Hurthle’s results, they made many of the experiments which 
he describes, and are able to corroborate his conclusions as to the 
construction of a delicate and accurate piston recorder. The piston 
must be thin, to minimize the friction in the tube; it must be of 
small diameter and be connected by a joint with the piston rod and 
the lever, so that it shall not tilt and bind ; the movable parts must 
be as light as possible, to avoid the effects of inertia and momentum. 
The instrument to be described meets these requirements. More- 
over, the movable parts have but one half the weight of those of 
Hurthle’s apparatus, namely, 0.34 gram. The greatest difficulty to be 
overcome in devising such an instrument lay in the necessity of 
having the piston rod connected with the piston by a light ball and 
socket joint. The piston must move freely in the tube, and yet 
follow readily the movements of the lever. Not only does the lever 
describe an arc as it moves up and down, but if it has the flexibility 
essential to prevent friction on the drum surface, it may readily be 
displaced a little to one side or the other, so as not to be exactly 
over the centre of the piston chamber. A simple hinge-joint, such 
as Jaquet used in his form of piston recorder, is not sufficient to 
ensure that the piston shall not bind, and, because of the increased 
friction, fail to respond to delicate changes in volume. This diffi- 
culty was overcome by the following device. 
A cylinder of plaster of Paris was cast, and then turned on a lathe 
to fit, but not too closely, a selected glass tube of about four mm. 
bore, which was to be used as the piston barrel. A depression was 
then bored in the exact centre of the end of this cylinder to a depth 
slightly greater than the diameter of the round head of a fine Carls- 
bad insect pin, no. 2, with a head of a little less than I mm. diam- 
eter and a shaft 1 mm. thick; this was to be used as the piston rod. 
From the end of the cylinder, thus prepared, a disk was cut, which 
was as thin as could be made and not be perforated by the hole IV. P. Lombard and W. B. Pillsbury. 
which had been bored to receive the head of the pin. The thickness 
of the disk was mm. To connect the pin piston rod by a ball 
and socket joint with this disk which was to serve as a piston, the 
disk was put on the table, the pin was placed vertically over it with 
its head in the hole, (see Fig. i), a drop of water was placed in the 
hole, and plaster of Paris was added to it, care being 
taken that the piaster did not spill down on the sides 
of the disk. When the plaster had set and before it 
had hardened, the pin, which was still pressed firmly 
into the hole, was given a rotary motion, so that the 
head should form a suitable socket for itself, and this 
movement was repeated from time to time until the 
plaster had hardened. This piston with its rod, be- 
cause of its lightness and the presence of the joint, 
proved more durable than might have been supposed, and was 
able to resist much abuse. The one employed by us at present has 
been in almost daily use for several months. The petroleum oil 
which was used to lubricate the piston, seemed to harden the plaster. 
Figure i. The 
piston and pis- 
ton rod slight- 
ly enlarged. 
It has been found that a piston with a ball and socket joint, almost 
as light and perhaps even stronger than that just described, can be 
made by turning out a light disk of ivory, hollowing it to form a thin 
walled cup, perforating the bottom of the cup with a hole the size 
of the insect pin to be used as the piston 
rod, bevelling both edges of the hole, 
and, finally, after putting the pin through 
the hole so that the head lies in the bot- 
tom of the cup, filling the cup with 
plaster of Paris. In this case, also, as 
the plaster hardens, the pin should be 
Figure 2. The lever. One half 
actual size. 
given a rotary movement and be allowed to form a socket for itself. 
A little plaster disk of this kind, connected with a light long pin by 
a ball and socket joint, may find a number of uses ; for example, it 
is a convenient means of connecting a frog’s heart with a recording 
lever. 
The lever of the piston recorder should be very light, in order that 
it shall not oppose the movements of the piston by its inertia, nor 
exaggerate them by acquiring momentum. This is absolutely indis- 
pensable, for the piston rests on a column of air in the tube, as Ellis 
says, as on a delicate spring. Further, the compressibility of the 
medium by which it is propelled, requires that it shall write on the A New Form of Piston Recorder. 
189 
recording surface with the least possible friction; it must, therefore, 
be flexible, so as to yield to the inequalities in the recording surface 
and at the same time be sufficiently springy to maintain a continuous, 
gentle pressure on the recording surface. Finally, although yielding 
readily to pressure applied horizontally it must be unyielding in the 
vertical direction, so that it may give an accurate record of the move- 
ments to which it is subjected. 
Having these requirements in mind, we constructed the lever as 
follows. A strip of phosphor-bronze, 0.06 mm. thick, 2\ mm. wide, 
and 100 mm. long, was shaped at one extremity to form a sharp 
writing point; the other end of the strip was then bent twice at right 
angles upon itself, and the pin, 
which was to serve as the axis of 
the lever, was passed through 
holes bored in the shaft of the 
lever and in the end of the strip 
which had been bent parallel to 
it (see Fig. 2). The first bend 
was 82 mm. from the writing 
point, the second 11 mm. from 
the first. The holes for the axis 
were bored 76 mm. from the 
writing point, and were just large 
enough to permit the lever to 
turn freely on the medium sized 
pin that served as axis. Another 
smaller hole was bored through 
the shaft of the lever, 82 mm. 
from the axis, to form the bearing 
Figure 3. The piston recorder and its con- 
nections. One fourth the actual size. 
of the piston rod. This caused the movements of the piston to be 
magnified about nine times. The piston rod pin was bent at right 
angles 12 mm. from the piston, and then passed through the hole 
which had been prepared for it in the shaft of the lever. It was 
prevented from falling out by a second sharp upward bend (see 
Fig. 1). 
After the piston rod was attached to the lever, a drop of petroleum 
oil was put on the plaster of Paris piston, and then a bit of lead, 
which exactly sufficed to counterbalance the lever and moistened 
piston, was clamped on the horizontal back plate. The total weight 
of the counterbalanced lever, with Its pin axis, piston rod, and oiled 190 
IV. P. Lombard and IV. B. Pillsbury. 
piston, was 0.39 gram. A little cone-shaped washer of brass was 
put on the pin axis, with its apex towards the lever, to keep it from 
rubbing on the support of the axis. 
The pin used as the axis of the lever was supported by being 
passed through a hole near the extremity of a small horizontal brass 
rod, (a, Fig. 3), and secured by a binding screw in the end of the 
rod. This rod was in turn supported by a little clamp, (b), which 
fastened it to the horizontal arm of an L-shaped rod, the vertical arm 
of which was fastened by a clamp, (c), to a strong horizontal rod, 
(d), which was clamped near one end to an iron standard, (e), and 
carried at the other end a socket, which held the glass tube which served 
as the piston barrel, (/"). By suitable adjustment of these rods and 
clamps, the bearing of the piston rod could be brought directly over 
the centre of the glass piston barrel, so that the piston could move 
with the least possible friction. 
The records were taken on a Ludwig kymograph-drum, covered 
with highly glazed, very thin paper blackened with soot. That the 
friction of the writing point on the recording surface may be mini- 
mized, it is essential that it shall write at a tangent to it, and in a plane 
parallel to that of the drum. Further, it is very important that there 
shall be some device for rapidly adjusting the piston recorder, so 
that the writing point shall barely touch the surface of the drum. 
Either Boehler’s universal stand, Runne’s Basel stand, or some simi- 
lar contrivance will suffice to make this last adjustment quickly 
at any time during the experiment; the former we found very 
serviceable. 
The piston barrel was connected with the rubber tube leading to 
the plethysmograph chamber in one of two ways, each of which pre- 
vented the oil, which spread from the piston down the wall of the 
barrel, from entering the rubber tube. 
a. A short rubber tube connected the lower end of the piston 
barrel with a short glass tube, Qg), into the lower end of which had 
been sealed the slightly drawn out end of a second short piece of 
glass tubing. The space around this drawn out end acted as a catch- 
basin for the oil. The lower end of the second piece of glass tub- 
ing connected with the rubber tube which communicated with the 
plethysmograph chamber. 
b. The piston barrel was cemented into one of the short arms of a 
brass T-tube, which was so placed that the short arms were vertical 
and the longer stem horizontal. The horizontal stem was clamped A New Form of Piston Recorder. 
191 
to the standard, and carried a clamp which supported the rods which 
held the writing lever in place. The end of the lower short arm of 
the T was corked and acted as the catch-basin for the oil leaking 
down from the barrel. 
The thick walled rubber tube connecting with the piston recorder 
as described above did not communicate directly with the plethys- 
mograph chamber. It connected first with a short armed T-tube, 
which communicated, on the one hand, with a syringe, (//}, and on 
the other with a three-way stopcock (f). 
The syringe was air-tight, and it was possible, by movement of 
the plunger, to alter the amount of air in the system of tubes con- 
necting the recorder with the finger chamber. This is absolutely 
essential, in order that the changes of volume which are caused by 
temperature or by movements of the finger may be compensated, 
and the position of the piston recorder on the drum be adjusted. A 
large form of hypodermic syringe suffices; but, as very slight move- 
ments of the plunger cause large movements of the recording lever, 
it is best to solder the nut on the rod of the plunger to the syringe, 
and to move the plunger by screwing it in and out. 
The stopcock, (i), was connected not only with the 
piston recorder, but, by means of rubber tubing, with the plethys- 
mograph chamber for the finger. The third opening of the stop- 
cock communicated with the outside air. This arrangement made 
it possible to connect the piston recorder with the finger chamber, or 
either piston recorder or finger chamber with outside air. This was 
necessary, especially at the beginning of an experiment, when the 
finger was being introduced into the apparatus, and when the tem- 
perature of the air in the finger tube was changing rapidly. 
Experiments showed that it is important that the temperature of 
the finger should be kept as far as possible constant, especially 
during cold weather; moreover, in certain lines of work it is desira- 
ble to change the temperature suddenly. Two forms of apparatus 
were employed for regulating the temperature about the finger. In 
the first form, the tube containing the finger was surrounded by a 
jacket through which water of a known constant temperature circu- 
lated. The finger tube of this double walled plethysmograph cham- 
ber was ii|mm. long, and 2|mm, inside diameter; and it was open 
at one end to receive the finger, and closed at the other by a plate 
which was perforated by two small brass tubes. One of these tubes 
was connected by a stiff-walled rubber tube with the three-way stop- 192 
W. P. Lombard and W. B. Pillsbury. 
cock, and so with the piston recorder or the outside air; the other 
tube permitted the introduction of a thermometer into the finger- 
chamber. 
The brass jacket through which the water circulated was a little 
shorter than the finger tube. The open end of the finger tube pro- 
jected slightly beyond the jacket, and carried on its outside a flange 
which enabled the opening between the finger and the tube to be 
closed by a rubber membrane, sleeve, or glove finger, such as was 
employed by Mosso in his experiments with the sphygmomanom- 
eter. In our experiments, however, the opening between the 
finger and the brass tube was closed by a cork, as will be described 
later. A system of reservoirs and tubes permitted the finger to be 
subjected to a known constant temperature, and allowed the tem- 
perature surrounding it to be changed quickly to any desired degree. 
The second method permitted the finger to be kept at a constant 
temperature, but did not allow of sudden changes of temperature. 
In this method the finger plethysmograph consisted of a glass tube, 
closed at one end by the finger cork, and at the other by a cork 
through which a thermometer and the glass tube connecting with 
the piston recorder passed. A coil of fine wire was wound many 
times around the glass chamber, and when an electric current was 
turned on, heated the chamber. The temperature was controlled 
by means of a rheocord, which permitted the flow of the current to 
be regulated. During summer weather, the room temperature is 
sufficiently high and constant for ordinary investigations, and these 
methods of heating are unnecessary. It is sufficient to enclose the 
finger in a test tube drawn out at one end for the attachment of the 
tube connecting with the piston recorder. In all cases it is neces- 
sary to protect the subject, the plethysmograph chamber, and the 
system of air tubes connecting the plethysmograph chamber with 
the recorder, from sudden changes in temperature. The whole 
arrangement forms a very delicate recording thermometer, and, if 
not guarded, may give false results. Ellis speaks of this, and in 
some of his experiments used a second, control apparatus. We 
have found that for experiments which last only a short time and 
are taken with suitable precautions this is unnecessary. 
Method of closing the opening between the finger and the reservoir. 
One of the greatest sources of error to be encountered in plethysmo- 
graphic experiments arises from the fact that movements of the arm, 
be they caused by changes in the tension of the muscles or by some A New Form of Piston Recorder. 
form of movement of the trunk, as in respiration, tend to cause move- 
ments of the finger in the plethysmograph, not always to be dis- 
tinguished from changes in volume of the finger. As a change of 
even less than \ cubic millimetre in volume is recorded by the piston 
recorder, it is evident that the utmost care must be taken to secure 
a constant position of the finger as respects the plethysmograph. 
On account of the mobility of the skin on parts beneath, the arm 
and hand cannot be fixed absolutely by splints, casts, etc., and if the 
plethysmograph chamber be fastened to a firm support it is impos- 
sible to prevent the finger from moving in the tube. To overcome 
this difficulty it is necessary to resort to the principle first employed 
by Chelius, and rediscovered by Mosso, who employed it in his 
arm plethysmograph, namely, the suspension of the plethysmograph 
chamber and the arm by a long cord, so that they will move freely 
and yet together. Even this method is imperfect, in case the space 
between the finger and the plethysmograph be closed by a rubber 
membrane or sleeve. 
The best way to close the opening between the finger and plethys- 
mograph tube, is to put on the finger a cork ring which exactly fits 
the plethysmograph tube. Such a ring, if made to fit the finger 
only moderately tightly, offers considerable resistance to the move- 
ment of the finger, and, if smeared with vaseline, readily gives an 
air-tight closure, without impeding the circulation. 
Apparatus for testing the delicacy and accuracy of piston recorder. 
In many of the plethysmographic records taken from the finger not 
only pronounced pulse curves were obtained, but these curves some- 
times showed marked secondary waves, similar- to those seen in 
ordinary sphygmographic tracings. The question of course pre- 
sented itself, are the dicrotic and other waves shown in the record 
a true expression of changes in volume of the finger, or are they 
artificial, i. e. caused by vibration of the air or oscillations of the 
recording apparatus? To decide this question an apparatus was 
constructed which should mechanically change the volume of the 
air in the tube connected with the recorder, at about the rate and 
degree indicated by the pulse waves. A stiff brass lever was fas- 
tened firmly to a steel axis, which moved on screw bearings. The 
lever rested on a specially devised cam which was supported by an 
axis which carried a pulley driven by an electric motor. On the 
lever was a short pillar of brass. The pillar projected slightly into 
the lumen of a somewhat larger glass tube, supported just above it. W. P. Lombard and IV. B. Pillsbury. 
The opening of the glass tube was closed by gold beater’s skin, kept 
flexible by being moistened with water. When the cam was revolved, 
the pillar moved up and down, carrying with it the loose fold of 
gold beater’s skin, and so caused a rhythmical change in volume in 
the chamber of the glass tube. The upper end of the glass tube 
was connected by a stiff-walled rubber tube with the piston recorder, 
and the movements of the air column in the glass tube were re- 
corded by the piston recorder on a kymograph-drum. 
In the experimental tests made with this apparatus, to determine 
the effect of changes in the volume of the air in the tube upon the 
movement of the piston recorder, the brass lever was sometimes 
moved by the hand, the end of the lever being held between the 
thumb and forefinger, and, sometimes, by rotating the cam upon 
which the lever rested. These tests revealed the following facts. 
Slow changes in volume, even if extensive, are recorded accurately. 
Rapid changes in volume, if extensive, may lead to a slight throw 
of the lever. Changes in volume of the rate and extent of those oc- 
curring in the finger, whether caused by vasomotor, respiratory, or 
pulse movements, are recorded accurately. The question which most 
interested us, was whether the record of changes in volume as exten- 
sive and rapid as those resulting from pulse movements, would show 
oscillations that might be confused with the dicrotic and other 
secondary waves which often appear in the pulse curve obtained from 
the finger. A form of cam was chosen such as would give a sudden 
upward movement and a slow fall of the brass lever. The changes of 
volume recorded were somewhat more extensive than those caused 
by the pulse, and a rate of rotation was readily obtained by the motor 
which gave a more rapid change of volume than the pulse records 
showed. To be sure of our facts, we took two records on the same 
drum, the one of the artificial pulse, obtained from our testing appa- 
ratus, and the other, of the normal finger pulse. The pressure of the 
piston recorder lever was the same in both cases. It was found that 
changes in volume, which were considerably more rapid and exten- 
sive than those caused by the pulse, did not show any throw of the 
recording lever or any secondary oscillations, and we assured our- 
selves that the dicrotism and other oscillations which are recorded in 
the normal pulse curves from the finger, do not originate in the re- 
cording mechanism (see Fig. 4). It was found further, that if the 
cam of the testing apparatus was revolving at a regular rate, and the 
air in the apparatus was rhythmically carried forwards and backwards A New Form of Piston Recorder. 
by movements of the adjusting syringe, a combination curve, closely 
resembling the pulse and respiration curves obtained from the finger, 
could be produced. This makes it possible to study the effect of 
respiratory changes in volume upon the shape of the pulse curve, a 
question of importance. 
Latent period of the piston recorder. This was determined empiri- 
cally to be but slightly over Too second, and was found quite constant 
for both a decrease and an increase in the volume of the air. It was 
tested by connecting two piston recorders, or a piston recorder and 
a tambour, writing on 
the same drum, by a 
stiff-walled rubber tube 
one metre in length, a 
length somewhat greater 
than that used in our 
plethysmographic ex- 
periments. If the tam- 
bour lever or the lever of 
one of the piston re- 
corders was suddenly 
moved, the piston re- 
corder under observa- 
tion was found to start 
about xlu second late, 
and to lag at the crest 
of the curve, at the most, 
to second. This lag de- 
pended on the extent 
and rate of the change 
of volume, and was due to friction of the lever on the drum, com- 
pression of the air column, and displacement of the oil about the 
piston. The displacement of the oil, seen when the movements were 
extreme and rapid, was only momentary, as capillary force drew the 
oil back. This error need be feared only when the movements re- 
corded are more rapid and extensive than those which result from 
ordinary changes in the volume of the finger. The figures here 
given apply to movements very much more rapid and extensive than 
those caused by the volume changes of the finger due to the pulse, 
etc. We concluded from our experiments that such records as are 
obtainable from the finger, are accurate to within second, if the 
Figure 4. One half the original size. The upper- 
most curve, taken June 5, 1899, on a warm day 
(room temperature, 290 C.), from the two first pha- 
langes of the left hand. The time, in seconds, is 
, , . , ~ t , 
recorded at the bottom of the tracing, xhe lowest 
curve, an imitation of a pulse tracing, was obtained 
by using the apparatus described on page 193. 196 
W. P. Lombard and W. B. Pillsbury. 
lever is adjusted properly. In this connection, however, it is neces- 
sary to express again the warning that any undue friction of the 
lever upon the drum is liable to delay the rate and lessen the extent 
of the movements of the recording lever. 
Calibration of the piston recorder. -—As a further test of the delicacy 
of the apparatus, we measured the change in the volume of the air 
that corresponded to the movement of the lever. To this end, move- 
ments of the lever were compared with the movements of a column 
of mercury in a tube of small bore, attached to the piston recorder. 
The volume of the tube used was ascertained first by filling the tube 
with mercury, and secondly, by weighing the tube when filled with 
mercury and when empty, and reducing from weight to volume, with 
suitable corrections for temperature. The results of the two methods 
agreed very closely. The uniformity of the bore of the tube was es- 
tablished by the fact that the same amount of mercury occupied 
equal lengths for all parts of the tube; one centimetre of the tube 
held 9.1 cubic millimetres of mercury. One end of this tube was con- 
nected by a rubber tube with the main tube of our apparatus, and to 
the other end was attached a small piece of rubber tubing filled with 
mercury and closed by a pinch-cock. The length of the column of 
mercury in the capillary tube was varied by compressing this short 
rubber tube between two bits of wood held in the jaws of a burette 
clamp. The length of the column was read on a scale and compared 
with the record on the drum. The result showed that a movement 
of one centimetre in the mercury in the tube would induce a move- 
ment of the lever of 5.7 millimetres, i. e., that one millimetre on the 
drum corresponded to a change in volume of 1.6 cubic millimetres. 
Furthermore, a change of less than \ millimetre in the tube, or con- 
siderably less than \ cubic millimetre was found to produce an 
evident movement of the piston recorder. This also confirmed the 
previous results, inasmuch as different changes in the length of the 
column of mercury were always accompanied by relatively equal 
movements of the lever. 
The pulse oscillations recorded in Fig. 4 bear witness to the 
capacity of our instrument. They were taken on a hot day, when 
the blood-vessels of the finger were largely dilated. This curve 
shows also Traube-Hering waves. The dicrotism exhibited was not 
due to the apparatus. In the artificial pulse shown in Fig. 4 the 
pulse movements were no less high and steep than those obtained 
from the finger, but they are free from secondary waves. A New Form of Piston Recorder. 
197 
Another indication of the delicacy of the piston recorder for 
changes of slight intensity, was given by the fact that the capillary 
attraction for water in a tube with a bore of 1 mm. was strong enough 
to produce marked movements of the lever. 
Method of class etc. —lt is not difficult to employ 
the piston recorder in demonstrations before large audiences. If a 
small silvered cover glass be fastened in the place of the counter- 
balancing weight on the back of the lever, a beam of light can be 
thrown on a screen, and the ordinary changes in the volume of the 
finger caused by the pulse and respirations can be shown. The effect 
of reflex excitations, such as the application of ice to the skin of the 
other hand, may also readily be exhibited. 
A Statement of some of the Facts observed with 
the Piston Recorder. 
The account which we have given of the piston recorder was 
written six months ago, and since that time we have had occasion to 
make frequent use of the instrument. Our experience has only con- 
firmed our opinion that the instrument, in spite of its apparent deli- 
cacy, is very durable, and with proper handling is capable of giving 
valuable results. 
It may be of interest, as showing the value of our method, for us 
to enumerate some of the more salient physiological facts which 
have attracted our attention during our preliminary tests of this 
apparatus. 
All of the tests were made with only two phalanges of the first or 
second finger of the left hand. When one of these was inserted into 
the plethysmograph chamber, the heat of the finger caused a rapid 
expansion of the air in the chamber and the system of tubes con- 
necting it with the recorder. A considerable time was required for 
an equilibrium to be established between the heat of the finger and 
the temperature of the surrounding air. During this period of ad- 
justment, the piston lever was kept level, either by gradually drawing 
out the piston of the adjusting syringe, and so enlarging the space, 
or by turning the three-way stopcock so as to give free communica- 
tion with the outside air. As the constant rise of the piston lever 
due to the expansion of the air lessened, the fluctuations of the vol- 
ume of the finger became evident. These volume changes were 
manifested by quick up-and-down movements of the lever due to the 
pulse, slower rhythmical movements which correspond to respiratory 198 
JV. P. Lombard and W. B. Pills bury. 
movements, and much slower variations, presumably produced by 
vasomotor changes. 
The extent of all of these fluctuations was very markedly influenced 
by the temperature to which the body as a whole, and more es- 
pecially the finger under observation, was exposed. If the room was 
cold, the volume changes described were hardly perceptible, while in 
a warm room all three of these changes showed themselves. The 
difference between the size of the variations in summer and winter 
was very great. The general effect of the room temperature on the 
body could be counteracted in part by changing the temperature of 
the finger. When 
the temperature of 
the room was low, 
and the fluctua- 
tions were barely 
visible, it was pos- 
sible to carry on 
experiments by 
raising the tem- 
perature of the air 
in the finger cham- 
ber to about 34° C. 
On the other hand, 
it was found that 
changes in volume 
that were fairly 
well marked in a 
Figure 5. One third the original size. Plethysmographic 
record from two phalanges of middle finger of left hand, 
May 1, 1899. Height of piston lever, when horizontal, 
above bottom of seconds tracing =34 mm.; height of respi- 
ration lever, when horizontal, above bottom of seconds 
tracing =75 mm.; length of piston lever, 70 mm. ; length of 
respiration lever, 93 mm. Respiration lever wrote 0.8 mm. 
to the right of the piston lever. Subject stated at the close 
of experiment that he had caught himself thinking actively 
of his work, and had tried to stop thinking. 
moderately warm room, would become greatly lessened, or entirely 
disappear if the temperature of the air about the finger were lowered 
to about 20° C. We can confirm the results of Mosso, Frangois- 
Franck, Sewall, Sanford, and others, that cold applied to the other 
hand noticeably decreases the volume of the finger under observa- 
tion. Thus when the right hand was dipped into cold water there 
followed a marked shrinkage of a finger of the left hand, and the 
extent of the oscillations of volume due to the pulse, respiration, etc., 
greatly decreased. 
Very similar results accompanied the pain caused by stimulating 
the skin of the other hand with an induced current. Two to three 
seconds after the stimulus was applied, there was a marked shrinkage 
of the finger, and the height of the pulse oscillations lessened. A New Form of Piston Recorder. 
199 
These effects seemed to be common to nearly all the psychical and 
reflex disturbances that were noticed. The odor of a stale cigar held 
under the nose, pulling a hair, blowing in the face, and other minor 
persecutions, invariably gave the same result. During the progress 
of the experiments, the mind of the subject would very frequently 
drift to some problem of daily routine or one connected with the ex- 
periment. At such times the volume of the finger would show a 
marked fall (see Fig. 5), The only two exceptions to this rule were 
both at times when the mental state was one of amusement; once at 
a remembered event, the other time, over an incongruous conjunction 
of ideas in the train of thought. In these two cases a well marked 
and long continued rise was observed. 
Sudden changes in respiration produced a very pronounced varia- 
tion in the ordinary course of the experiments. A partly suppressed 
yawn, followed by a long expiration, for instance, was accompanied 
by a fall in the height of the lever. The effects of Valsalva’s and 
Muller’s experiments to cause a weakening or temporary cessation 
of the pulse, were, of course, at once evident. 
In addition to recording changes in the circulation caused by 
forced respiratory movements, the instrument gave a striking pic- 
ture of the normal variations in the volume of the hand when the 
subject was at rest. By recording the respiration with Marey’s 
pneumograph, just over the piston recorder tracing, it was possible 
to notice the time relations of the movements of the wall of the chest 
or abdomen and the corresponding oscillations of the volume of the 
finger. These changes of volume were seen to hold about the same 
relation to the breathing movements, as has been observed for res- 
piratory fluctuations of the blood pressure. The volume begins to 
increase at about the middle of inspiration, and continues to rise 
until about the middle of expiration; it then falls during the latter 
part of expiration and the beginning of inspiration. This general 
correspondence is, however, subject to wide fluctuations. The effects 
of respiration were usually shown when the volume of the finger was 
large. No constant relation, however, was seen to exist between the 
size of the pulse and the respiratory oscillations. Sometimes the 
pulse oscillation would be fairly large when no respiratory change 
was to be seen, and, at other times, there would be well marked 
respiratory oscillations when the pulse movements were scarcely 
visible. 
The height of the pulse wave was very plainly influenced by the 200 
W. P. Lombard and W. B. Pillsbury. 
volume of the finger. By large volumes the oscillations were rel- 
atively small, by medium they were greatest, while by small 
volumes they were very small or altogether disappeared. As the 
volume changed from large to medium, the downward oscillations 
were the first to increase in size and vice versa. 
In the pulse wave the dicrotism quickly attracts attention. 
The dicrotism was seen to undergo marked variations, and our 
method bids fair to contribute important facts as to the origin of the 
secondary waves and the influences affecting them. A propos of the 
discussion as to the origin of the dicrotic wave, it is worthy of note 
that this wave is clearly to be seen in experiments, such as ours, 
which deal with the phenomena of the extreme peripheral circulation. 
In addition to the pulse and respiratory changes in the volume of 
the finger which have been described, still another change, having 
a much longer period, was observed. The duration of these longer 
waves was from seven to ten seconds from crest to crest, which 
makes it probable that they were of the same type as the Traube- 
Hering blood pressure waves. 
Still another series of facts exhibited by our tracings relate to 
the periodic changes in the rate of the heart. The pulse rate was 
found to vary with the respiration. It was higher during the latter 
part of expiration, and lower during inspiration. Moreover, in some 
cases, when the breathing was suspended, this rhythmic change in 
the beat of the heart showed a tendency to persist. Still another 
rhythmic change in the rate of the pulse, recurring in longer periods, 
was noticed at times. 
The facts which we have here stated may suffice to indicate the 
value of the piston recorder, not only as a means of demonstrating 
many important circulatory phenomena but as giving to the plethys- 
mographic method an added delicacy.