110 Messrs. T. L. Brunton and J. Fayrer on the [Jan. 22, 



inhibitory centres, by the division of the medulla having no power to in- 

 crease the reflex action. 



The fact that irritation of the lumbar nerves hardly caused any contrac- 

 tion 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 paralyzed 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 dis- 

 tinguished 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 ex- 

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

 the diminution of reflex action is due to the latter of these causes. 



Experiment LIU. 



May 19^, 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. Bight arm twitched. 



3.57. Beflex action in both arms. None in the legs when the left leg is 

 dipped in the acid. 



4. No reflex action from ligatured leg. 



4.2. No reflex action from left leg in 60 seconds when it is dipped in 

 the acid. 



4.10. No reflex action from either leg in 250 seconds. 



The medulla was now divided in order to separate the cord from 

 Setchenow's inhibitory centres. 



4.35. No reflex action can be observed. 



As the operation of dividing the cord somewhat lessens the excitability, 

 in the following experiment the division was performed on the previous 

 day, so that its effects should have passed off before the poison was injected. 



The columns headed " left " and " right" indicate the number of seconds 

 which elapsed before the corresponding leg was drawn out of the acid. 



