EFFECTS OF VENOM ON THE NERVOUS SYSTEM. 49 



Sensory and Motor Nerves. — In order to more directly test the action of venom 

 upon the motor and sensory fibres we exposed the sciatic nerve along the whole 

 extent of the thigh of pithed frogs, and placed in the middle of the exposed trunk 

 a little (Crotalus) venom (concentrated by spontaneous evaporation). Comparative 

 observations were now made from time to time by exciting the mixed nerve trunk 

 above and below the point of application of the venom by means of electrodes 

 connected with a Du Bois-Reymond induction coil, using minimum strengths of 

 current. After about fifteen minutes, irritation of the foot of the leg with the 

 poisoned nerve did not give as good reflexes as irritation of the other leg. , After 

 five hours, irritation of the trunk of the nerve below the poisoned part did not 

 give reflexes, but above the part did give reflexes, showing that the sensory fibres 

 were functionally destroyed by the local application of the poison. When the 

 trunk was irritated above the poisoned part marked contraction of the muscles of 

 the limb occurred, showing that the motor fibres and muscles were still intact. 

 After the lapse of six hours the motor nerves would no longer respond to stimulus, 

 although the muscles were still irritable. 



From these observations it seems obvious that both the sensory and motor nerves 

 are affected by the poison, and that the sensory nerves are far more susceptible 

 than the motor nerves, and that the depression of the sensory nerves may be con- 

 nected with the depression of reflex activity; but it seems more than likely that 

 the loss of reflex activity is essentially of spinal origin, since there is not a slow, 

 gradual diminution of reflex activity but a sudden paralysis — a characteristic which 

 may be considered almost exclusively spinal. 



The Spinal Cord. — We have already stated that the motor columns of the cord 

 remain irritable after complete paralysis of the sensory columns. We have 

 supplemented these observations by some experiments showing the direct action 

 of venom upon the exposed spinal cord, which prove that the motor columns them- 

 selves ultimately succumb to the poison. In two experiments made upon large 

 frogs, in which was laid bare the spinal cord in the dorsal region and in which 

 the animals were left to fully recover from the shock, a concentrated solution of 

 the dried* venom of the Crotalus adamanteus was placed on a small portion of the 

 cord. Before the application of the venom the cord responded actively to slight 

 mechanical irritation; after the application of the venom there occurred a gradual 

 impairment in irritability for the first fifteen minutes ; this impairment increased, 

 so that at the end of two hours the cord would not respond to moderate electrical 

 stimulus. The diminution of function continued until at the end of seven hours 

 the strongest current induced no response, although the motor nerve trunks 

 responded actively. 



Voluntary Motion. — Usually the earliest signs of nerve poisoning with venom 

 are a disturbance of coordination and loss of voluntary motion. In frogs we found 

 that as long as voluntary motion lasted the reflexes were active, but that with a loss 

 of volition reflexes were at once decidedly diminished and suddenly disappeared. In 

 frogs in which the abdominal aorta was ligated so as to prevent the poison from 

 affecting the nerves of the posterior extremities, the results were similar. 



In a number of observations made upon mammals the above conclusions were 



