€46 
DR. T. L. BRITNTON AND MR. W. PTE ON THE ACTION 
its administration is due to stimulation of the vagus-roots and not to stimulation of the 
inhibitory apparatus in the heart itself. 
It also shows that a large dose completely paralyzes the ends of the vagus in the 
heart, so that a strong interrupted current applied to the trunk of the nerve produces 
no slowing of the cardiac pulsations. 
Action of a small dose on the excitability of the Vagus. 
As it has been stated that digitalis in small doses increases the excitability of the 
ends of the vagus in the heart, so that a slight irritation applied to the trunk of the 
nerve will cause slowing or stoppage of the heart after the administration of the drug, 
although previously it had no effect, it seemed advisable to ascertain whether or not a 
similar action was possessed by casca. The following experiment was therefore tried : — 
Minimum Irritation of Vagus {peripheral end). 
Experiment XXXVI. — April 6. 
A cat, weight 6 lb., was chloroformed, and kept under chloroform the whole time of 
the experiment. 
A cannula was inserted into the right carotid artery and into the right femoral vein. 
Both vagi were then cut, and the peripheral end of the right vagus attached to Von 
Basch’s electrodes. 
Operation lasted half an hour ; the cat at first very feeble, afterwards recovered. 
Time. 
Blood- 
pressure. 
Oscilla- 
tions. 
Pulse. 
m. s. 
millims. 
millims. 
1 50 
Condition previous to irritation, both vagi being cut . . 
120 
1-2 
40 
2 0 
Right vagus irritated. Coil 30°. No effect 
[ 1201 
\ 125/ 
1-2 
42 
3 20 
Right vagus irritated. Coil 25°. This irritation was 
sufficient to slow the heart and lower blood-pressure 
100 
5 
20 
5 0 
Condition previous to injection 
155 
2 
44 
As the cat was stronger, the normal minimum irrita- 
bility was again tried, and coil 25° was again 
found to be the weakest which produced any effect. 
6 01 
1 \ cub. centim. casca solution, as in Experiment 
6 30 f 
XXXIV., injected into femoral vein. 
7 0 
Condition after injection 
175 
2 
42 
7 30 
Vagus irritated. Coil 30°. No effect 
175 
2 
40 
8 0 
Vagus irritated. Coil 25°. No effect 
180 
2 
42 
From this experiment it appears that the excitability of the peripheral terminations 
of the vagus-nerve is not increased by casca. 
Action on the Vagus-roots. 
The slowness of the pulse which quickly follows the injection of casca, and which we 
have already shown to be due to stimulation of the vagus-roots, might be caused either 
{a) by stimulation of the central end of the vagus by increased blood-pressure in the 
