POISON OF SOME INDIAN VENOMOUS SNAKES. 79 



In this experiment the loss of reflex motion was gradual. 

 It is shown to be due to paralysis of the cord, and not to 

 excitation of Setschenow's inhibitory centres, by the division of 

 the medulla having no power to increase the reflex action. 



The fact that irritation of the lumbar nerves hardly caused 

 any contraction in the legs, while irritation of the sciatics below 

 the ligature caused them to contract readily, indicates either 

 that the nerves had been injured by the ligature, or that the 

 part of them lying between the spine and the ligature had been 

 paralysed by the poison. The latter is possible ; but as the 

 frog moved its arms and not its legs before death, the former is 

 more probable. 



Several years ago Setschenow showed that the optic lobes in 

 the frog possess an inhibitory power over the reflex acts 

 originating in the spinal cord. Irritation of the optic lobes 

 greatly lengthens the time required for the performance of any 

 reflex act, and thus produces an effect apparently similar to 

 that of diminished excitability, or paralysis, of the spinal cord. 

 A diminution in reflex action may therefore be due to two very 

 different causes : — (1) Lessened excitability of the cord, and 

 (2) excitement of Setschenow's inhibitory centres. These can, 

 however, be readily distinguished from one another by dividing 

 the cord just below the medulla. It is thus separated from the 

 inhibitory centres ; and if the diminution in reflex action is due 

 to excitement in them it will disappear, but will be permanent 

 if it is caused by paralysis of the cord. The following 

 experiment, performed by Tiirck's method, shows that in cobra- 

 poisoning the diminution of reflex action is due to the latter of 

 these causes. 



Experiment LIII. 



May 19th, 1873. — The right leg of a frog ligatured, excluding 

 the sciatic nerve. 



3.5. A full dose of dried cobra-poison dissolved in water 

 injected into the dorsal lymph-sac. 



3.54. The animal appears dead. Both hind legs dipped into 

 dilute acetic acid. Eight arm twitched. 



3.57. Keflex action in both arms. None in the legs when 

 the left leg is dipped in the acid. 



