132 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



is a gradual diminution, and violent convulsions repeatedly occur. This 

 respiratory convulsion is interpreted by Rogers to be a sign that the 

 respiratory center, which otherwise would fail, is functionally revived by the 

 artificial respiration; hence convulsions. That the paralysis of the respiratory 

 center is not the only cause of asphyxiation, but that paralysis of the end- 

 plates of the phrenic nerves takes part in it, is experimentally shown by 

 Rogers both in cold-blooded and in warm-blooded animals. In cats and 

 rabbits, many times the minimal lethal doses were given intravenously, and 

 then the exposed phrenic nerves at the neck were stimulated by an interrupted 

 induced current at intervals of a minute. After the complete cessation of 

 respiration the phrenic nerves were stimulated, but found to be completely 

 paralyzed. Direct stimulation of the diaphragm gave a marked contraction. 

 It was, however, found that the respiration was much reduced in frequency 

 and amplitude several minutes before the weakening of the irritability of the 

 phrenics. It is interesting to notice that the end-plates of the sciatic nerves 

 remained excitable much longer than those of the phrenics, being still reactive 

 at the time of complete cessation of circulation. 



Rogers also tested the comparative sensitiveness of the nerve-trunk and 

 nerve-ending to the paralyzing action of the venom. Here, using frogs, he 

 employed the venom in dilution of i : io 8 to 10 s , subjecting the nerves to its 

 action for i to 5 minutes in strong and up to 1 hour in weak solution. No 

 deteriorating effects on the irritability of the nerve-trunk were observed, but 

 that of the nerve-ending was totally lost. Even a 1 per cent solution of the 

 venom of Enhydrina acting for 5 minutes had no effect on the nerve trunk. 



In regard to its action on the reflex functions of the spinal cord, Rogers 

 points out that it is slight and altogether secondary in importance to its in- 

 fluence on respiration. He states that the venom of Enhydrina in 1 : 100 

 solution has no appreciable effect when applied directly to the frog's heart, 

 whereas a few drops of a 1 : 1000 solution are quickly fatal when given 

 intravenously. This seems to present a great difference from the venoms of 

 Pseudechis, Naja, and Trimeresurus. 



Fraser and Elliot, 1 working with the venoms of Enhydrina valakadien and 

 Enhydris curtus, mention the occurrence of motor end-plate paralysis in the 

 enhydrina poisoning. They also made direct application of the venom to 

 the region of the respiratory center and found it quickly fatal without affect- 

 ing the circulatory system at the same time. On application of the venom 

 directly to the exposed hearts (in situ) of mammalia no effect was observed 

 on the vagal cardio-inhibitory center. The vasomotor center is also un- 

 affected by this venom. 



1 Fraser and Elliot. Contributions to the study of the action of sea-snake venoms. Roy. Soc. Proc. , 

 1904, LXXIV, 104. 



