ON THE MAMMALIAN NERVOUS SYSTEM. 



461 



excitation of the two posterior columns are concerned, the above experiments give 

 results which are fundamentally the same as those obtained in the mixed nerve. On 

 the other hand, the lateral column effect is almost entirely wanting in these 

 experiments. The alterations in the excitability of the posterior root itself may be 

 to some extent responsible for this, and in any case should, if possible, be excluded. 

 In order to carry out this exclusion, experiments were performed in which, whilst 

 investigating the effect in the mixed sciatic nerve, the (motor) efferent paths were 

 annulled by section of all the anterior roots of the lumbar plexus. 



(2.) Effects in the Sciatic Nerve after Section of Anterior Roots. 



This experiment we have performed on two animals (Cats), in each of which 

 the cord was divided and exposed for excitation at the level of the llth dorsal 

 vertebra, and the left sciatic nerve prepared in the usual way for connection with the 

 electrodes. The lower lumbar cord and the cauda'equina were then exposed in each 

 animal by opening the canal for about 5 centims. The anterior roots of the left 5th, 

 6th, and 7th lumbar, and 1st and 2nd sacral nerves, were cut within the canal. 

 All other connections were then divided, so as to leave the left sciatic nerve in con- 

 nection with the cord by the posterior roots only. 



The excitation of the cord proceeded in the usual manner, but a " maximal " intensity 

 of stimulus alone was employed, and the time of stimulation was 7 seconds. 



EFFECT in Left Sciatic Nerve after Division of its Anterior Roots. 



From these figures it will be seen that the effect evoked in the sciatic nerve by 

 excitation of the posterior column on the same side was more than twice us large as 

 that resulting from excitation of the posterior on the opposite side and more than 

 four times as large as that due to the lateral on the same side. 



In another animal the same anterior roots were divided, and in addition all the 

 posterior roots on the left side and all nervous connections except the 7th lumbar 

 posterior root, thus leaving the left sciatic nerve as a mere continuation of this 



