48 THE VENOMS OF CERTAIN THAKATOPHIDEil. 



CHAPTER V. 



THE EFFECTS OF VENOM ON THE NERVOUS SYSTEM. 



Excepting as regards the marked action on the respiratory centres we cannot 

 consider venom as essentially or solely a nerve poison. In animals which do not 

 immediately die from the effects of this poison, the first signs of nerve poisoning 

 are drowsiness, incoordination, followed hy loss of voluntary motion, by convul- 

 sions, or failure of reflex activity and by death. 



Reflex Action. — In six experiments on frogs with the Crotalus, made in connec- 

 tion with a direct study of the effect on reflex action, in none of them was there 

 found a slow, gradual diminution of reflex activity, but invariably a sudden loss of this 

 function. The time of the occurrence of the loss of reflex activity varies very 

 greatly. In four experiments on pithed frogs, each of the frogs was given 0.015 

 gram of the dried Crotalus adamanteus venom in 10 minims of distilled water, 

 by means of injection into the posterior lymph sac. In one experiment no 

 alteration in reflex activity occurred after one and three-quarter hours, although it 

 seems probable that the venom was not by any means completely absorbed since 

 the lymph sac seemed bulged with fluid which had accumulated. In another 

 experiment no alteration occurred in one and a half hours. In a third reflex action 

 was suddenly abolished in one hour, and in a fourth in forty-five minutes, without 

 there being in. any case gradual diminution of reflex activity preceding the com 

 plete loss. 



Two experiments were made on pithed frogs to determine if the loss of reflex 

 activity was due to an action of the venom upon the nerves or upon the spinal 

 cord, and for this purpose we ligatecl all of the bloodvessels in the right hind leg 

 of each animal, and thus prevented the access of the venom to these parts. To 

 each of these frogs was given 0.015 gram of the dried venom of the Crotalus 

 adamanteus dissolved in 5 minims of distilled water, and injected into the posterior 

 lymph sac. Reflex activity suddenly ceased in both of the frogs in one and a half 

 hours. No reflex action was elicited by irritation of the nerves of either leg, 

 although the motor fibres of the nerves were very excitable. We also found that 

 direct excitation of the spinal cord in the dorsal region produced movements in 

 the posterior extremities, but none in the anterior extremities, thus showing that 

 impulses could travel down the cord through the motor apparatus but not upwards 

 through the sensory portions. These observations make it clear that the loss of 

 reflex activity is, no doubt, dependent to a great extent at least upon an action of 

 the venom upon the sensory portions of the cord, although it is not clear that the 

 sensory nerve fibres may not also be seriously affected. 



