124 THE VENOMS OF CERTAIN T II A N A T O P H I D E &. 



In none of these experiments do we find a primary increase in the respiration 

 rate, as in animals with intact vagi, but invariably a diminution. It seems clear, 

 therefore, that the first result must be dependent upon an excitation of the peri- 

 pheries of the pneumogastric nerves, and that the diminution of respirations is 

 due to a centrally active cause. Should the lessened number of the respirations be 

 central, that is, dependent upon a depression of the respiratory centres, we would 

 expect to find that the degree of depression would depend upon the relative amount 

 of venom coming in contact with these centres in a given space of time. We have 

 accordingly made an experiment, in which this suggestion is admirably carried out 

 by injecting the venom into the carotid artery, thus throwing the poison directly 

 upon the respiratory centres. 



Experiment No. 15. 



It seems obvious from the preceding experiments that venoms exert a double 

 action on the respiration ; first, an irritant action on the peripheries of the pneu- 

 mogastric nerves, by which an increase in the respiration rate is brought about ; 

 and secondly, a depression of the respiratory centres, by which the respiration 

 rate is diminished. Since the diminution in the respirations occurs in animals with 

 cut pneumogastrics immediately after injection, and at a time when an increase 

 occurs in normal animals, it is apparent that these two factors are acting in normal 

 animals at the same time to produce opposite results ; consequently, whether we 

 have an increase or a decrease in the respirations must be dependent upon the 

 relative degree of power exerted by one or the other of these factors. In most 

 cases we have found a primary increase of respirations followed by a diminution ; 

 it is therefore obvious that the action of the venom upon the peripheries of the 

 pneumogastric nerves was more than able to compensate for the depressant action 

 of the poison upon the respiratory centres ; this is very clear since no increase of 

 respirations above normal occurs in animals with cut pneumogastrics. In the two 

 cases in normal animals in which a decline from the first was observed, and in 

 which the animals died in a few minutes after injection, the action of the venom 

 upon the respiratory centres was so profound that the accelerator factor was unable 

 to cause a rise. This is also illustrated in the experiment in which the venom was 

 injected into the carotid artery and thrown upon the respiratory centres. 



Since venom does not seem to exert other than a depressant action upon the 

 respiratory centres, it does not appear probable that it would have an opposite 

 effect upon the respiratory nerves, so that the effect of the venom upon the peri- 

 pheries of the pneumogastric nerves is probably one of irritation rather than stimu- 



