266 ANIMAL PHYSIOLOGY. 
unexceptionally) different, the precise result being variable, but 
generally the beat is both accelerated and increased in force. 
b a 
AU IU 
<—ex 
Fig. 238.—Inhibition of frog’s heart by stimulation of the vagus nerve. To be read from right 
to left. The contractions of the ventricle are registered by a simple lever resting on it. - 
The interrupted current was thrown in at a. Note that one beat occurred before arrest 
(latent period), and that when standstill of the heart did take place it lasted for a consider- 
able period (Foster). 
We may say that the working capacity of the heart is tem- 
porarily increased. 
6. The improvement in the efficiency of the heart is in pro- 
portion to its previous working power, and in cases when the 
, 
SS 
Stimulation Vagus. 
Fic. 239.—Effects of vagus stimulation, illustrated by a form of sph: ographic curve derived 
from the carotid of a rabbit (Foster). Peo ae 
action is feeble and irregular (abnormal) it might be said to be | 
in proportion to its needs. This is a very important law that 
deserves to receive a general recognition. 
7. Section of both vagi nerves results in histological altera- 
tions in the heart’s structure, chiefly fatty degeneration, which 
must, of course, impair its working capacity and expose it 
to rupture or other accidents under the frequently recurring 
strains of life. 
