574 
DE. SANDEESON ON THE INFLUENCE EXEECISED BY THE 
ordinary circumstances are very inconsiderable, are manifestly increased whenever the 
influx and efflux of air are obstructed*. 
Part II.— EXPEEIMENTS. 
The inquiry was commenced in 1864 and continued at various periods during 1865 
and 1866. Dogs were exclusively employed. On account of the mobility of their chests, 
and the great variety they exhibit in the mode of breathing, these animals are especi- 
ally adapted for the purpose required. In every instance the respiratory movements 
and the changes of arterial pressure were recorded mechanically on paper moving hori- 
zontally by clockwork. 
1. Description of the Apparatus. 
a. Respiratory movements . — For the purpose of recording the respiratory movements, 
a disk-shaped bag of caoutchouc about 6 inches in diameter is used. In the earlier 
experiments the material employed was vulcanized, but subsequently non- vulcanized 
india-rubber was preferred. Each of the opposite sides of the bag is glued to a circular 
disk of wood, which being of smaller circumference leaves a free margin of half an inch 
round the edge. Of the two boards the lower is fixed, the upper moveable. The latter 
is screwed to a double horizontal arm of whalebone, the effect of which is to support it 
horizontally about half an inch above the level of its fellow. By means of this arrange- 
ment the expansive and vertical movements of the bag are limited in such a manner 
that an equal resistance is afforded by the elastic whalebone to the ingress and egress of 
air. The centre of the moveable disk is connected, by means of a vertical rod, with a 
lever of the third kind, which is made of light wood terminating in whalebone, and has 
a total length of 25 inches. The lever works on a steel axis fitted to it by a socket of 
brass ; the axis is supported by a framework of brass which slides up and down on two 
rectangular brass rods, and is so arranged as to be readily adjusted and fixed by a screw 
at any desired height. The lever bears at its extremity a fine sable brush which is 
fixed horizontally at right angles to its length. Communication is made between 
the respiratory passages of the animal and the caoutchouc bag by a f -shaped tube of 
* The present state of opinion on the question may be gathered from the following quotations from the most 
recent physiological works : — 
“ During expiration the external surface of the heart is subjected to a stronger pressure than during inspiration, 
which is expressed in the greater frequency of its pulsation and in the rise of the mercury in the dynamometer.” 
— Budge, Lehrhuch der spec. Physiol. 1862, p. 350. 
After referring to the most recent researches, particularly those of Maret, the editor of the last edition of 
Dr. Carpenter’s ‘ Physiology ’ says, “ During the act of expiration the frequency of the pulse is considerably 
augmented, whilst the line of mean pressure rapidly rises, indicating increased tension in the arterial walls. .... 
During the act of inspiration, on the contrary, the pulsation becomes slower, the curves much bolder, and the 
line of mean pressure gradually falls ; for then the blood readily enters the thorax, and, as a consequence, the 
great veins, capillaries, and arterial walls become comparatively flaccid.” — Carpenter’s Physiology, last edition, 
1864, p. 245. 
