590 
DR. SANDERSON ON THE INFLUENCE EXERCISED BY THE 
peculiar. Thus if you watch the movements of the thorax, you observe, first, that the 
chest is unnaturally dilated, and secondly, that in inspiration its further dilatation is per- 
formed slowly and with effort, and is immediately followed by an expiratory movement 
of so sudden and violent a character, that it resembles the collapse of an elastic bag or 
bladder distended with gas which takes place when its stopcock is opened. The inspi- 
ratory act, on the other hand, is not only slow but comparatively fruitless ; for although 
the animal breathes so much less frequently than before, the quantity of air taken in at 
each expiration is scarcely, if at all, increased*. As regards the action of the heart, it 
does not appear to have been noticed by physiologists that the acceleration is not the 
only result produced ; along with the increased frequency there is a great increase of the 
arterial pressure, amounting in some instances to 2 or 3 inches. This effect, although it 
occurs immediately after the operation, is a continuous one, and may be observed at any 
time after its completion. 
The experiments on which these statements are founded were made at various periods 
during the last two years. I submit the tracings of two observations, made severally on 
the 29th of July and the 1st of August, 1865. 
Observation XVII. — July 29th (Tracings not engraved). 
The animal employed was a large, rough, mongrel terrier (male). The rate of move- 
ment of the paper was 1 inch in 7‘4 seconds. The experimental procedure was the same 
as usual, with the exception that the two pneumogastrics were exposed low in the neck, 
and ligatures passed round each of them. Immediately before dividing the nerves the 
animal was breathing tolerably regularly fifteen times per minute, the arterial pressure 
being 5 inches and the rate of the pulse seventy-eight. Six seconds elapsed between the 
sections of the two nerves. After the division the respiratory movements became irre- 
gular and then excessive, the arterial pressure increasing at once to 6 ‘2 inches. In less 
than half a minute after the first nerve was divided the breathing had again become 
regular, but had diminished in frequency to nine per minute, and had assumed the cha- 
racter usually observed after section. So long as the respiratory movements were regu- 
larly performed the mean arterial pressure remained unaltered, the variations during 
each respiratory act being as follows : — the highest point coincided with the end of 
expiration ; the pressure then sank during a period of about four-thirds of a second, 
then gradually rose until the commencement of the next expiratory act, which was 
accompanied by a much more decisive increase of arterial tension, lasting for about two- 
thirds of a second. Immediately after section of the first nerve the frequency of the 
pulse increased to 150, and subsequently to 165, which latter rate was maintained. 
After a time the respiratory movements became irregular, occasionally, however, resuming 
their original character. The irregularity principally consisted in the increased extent 
and frequency of the inspiratory movements, in consequence of which the arterial pres- 
* This statement is founded on the observations of Rosenthal, “Die Atherubewegungen und ihrer 
Beziehungen zum Ncrvus Vagus,” p. 109 et seq. 
