580 
DR. SANDERSON ON THE INFLUENCE EXERCISED BY THE 
Observation X. — June 28th, 1865. 
A full-sized male mongrel. Rate of movement 1 inch in six seconds. The animal 
struggled excessively on being secured, and breathed during the period of observation 
120 times in a minute ; the frequency of the heart’s action being from 190 to 200. The 
respiration was occasionally interrupted by deep sighs, the effect of which on the arterial 
pressure is well shown in the tracing. Each sigh was acco.mpanied by an immediate 
and rapid increase of pressure, which was followed by a corresponding acceleration of the 
action of the heart*. 
Observation XI. — August 9th, 1865 (Plate XXIII. fig. 6). 
A male English terrier was employed in this experiment. The trachea was not 
opened, the communication between the air-passages and the caoutchouc bag being 
effected by means of a moist bladder tied over the snout. The mouth of the bladder 
w as adapted to the T tube already described. In order to ensure the animal’s breathing 
freely, the teeth were kept apart by a wooden wedge. Rate of movement 1 inch in 
three seconds ; respirations eighteen, pulsations sixty-four per minute. The observation 
illustrates the effect of a mode of breathing which, although not strictly normal, is fre- 
quently seen in the dog. The animal inspired suddenly, the time between each inspira- 
tion and its successor being for the most part occupied by a prolonged whine terminating 
in a short expulsive movement which was immediately succeeded by inspiration. During 
the whine the respiratory lever remained at the same level or ascended very gradually. 
As regards the arterial pressure, the tracing shows that in this instance the rapid rise of 
the mercurial column coincided with the commencement of the whine, and that it began 
to fall one or two seconds before inspiration, so that the period of decline corresponded 
to the last half of the period of expiration and to the whole of the period of inspiration. 
The preceding observations afford conclusive evidence that in dogs the expiratory act 
is not the cause of the elevation of the arterial pressure which is associated with each 
respiration, for they show that the elevation invariably commences and is sometimes at 
an end before inspiration is completed. It can therefore scarcely be doubted that the 
effect in question is due to the expansion of the chest ; for if not caused by expiration, 
there is no other possible agency to which it could be attributed. It is now necessary 
to show that the conditions of experiment, in so far as they were unnatural, were not 
such as to interfere with the natural performance of the respiratory function, and that 
whatever explanation is applicable to the phenomena recorded, must necessarily be 
equally applicable to ordinary breathing in the dog. 
The mode in which the animals were secured, and the contrivances employed for trans- 
ferring to paper the movements of the air in and out of the respiratory cavity, have been 
already described. It might be objected that the natural breathing would be interfered 
with, either Ijy the pain and terror of the operation, by the absence of the controlling 
influence of the larynx, or by the resistance offered to the influx and efflux of air in its 
* The animal was afterwards used for an experiment on carbonic oxide. 
