PHYSIOLOGICAL ACTION OF VENOM OF BLACK SNAKE. 259 
experiments in which the acceleration in rhythm and increase in 
amplitude of the respirations have been very pronounced, sever- 
ance of both vagi has had no influence upon the amplitude, and 
only a slight retarding effect upon the rate. The diminution in 
frequency of the respirations so produced, have not however been 
proportionately more than occurs after severance of the vagi in 
unpoisoned animals. I therefore conclude that the increase in 
respiratory activity which so frequently occurs after inoculation 
with Pseudechis venom, is due to a primary stimulating effect of 
this poison upon the respiratory centre. 
Sometimes these two phases of increased activity and diminished 
activity alternate, but the latter gradually obtains the ascendency. 
Eventually the respiratory movements become imperceptible, and 
unless artificial respiration be immediately resorted to, the animal 
dies of asphyxia. Just previous to the final cessation of all 
respiratory movement, it is not infrequently the case that the 
respirations occur in little groups separated by periods when the 
breathing is in abeyance. 
When the respiratory movements have ceased, the animal is 
- usually seized with afew feeble convulsions during which it makes 
Some inspiratory gasps of very considerable extent, showing that 
although the respiratory centre fails to respond rhythmically to 
the stimulus of blood of such venosity as to powerfully stimulate 
both the vagus and vaso-motor centres, it does still respond when 
this becomes excessive, 
The more rapidly this cessation of the respiration is effected by 
the operation of the venom, the more powerful are the convulsive 
movements just preceding death. In cases of slow poisoning they 
are altogether absent, 
In Experiment 1 of this section, the respiration ceased before 
the efficiency of the circulation was in any way diminished. This, 
however, is not generally the case, and although suspension of the 
Tespiration usually precedes cessation of the heart-beat, the activi- 
es of both these mechanisms decline together. The gradual 
