466 MESSRS F. GOTCH AND V. HORSLEY 



examined at this later date, the animal was found to move in an ataxic manner, but 

 was not paretic ; the sensibility of the left hind limb was very much diminished, and 

 the left knee jerk was absent. 



The histological examination of the cord showed at the lesion on the left side 

 degeneration of (a) fibres entering the posterior cornu, (b) fibres in the posterior cornu, 

 (c) fibres in the posterior root zone, (d) fibres in the posterior external column. 

 Higher up, at the llth dorsal vertebra, there was no degeneration in the entering 

 fibres, but a large cornu-shaped patch of degeneration in the left posterior external 

 column. The left posterior median column showed no definite degeneration until the 

 lower cervical region was reached. 



The experimental results were obtained by dividing the cord at the level of the 10th 

 dorsal vertebra, and preparing both sciatic nerves for connection with the galvano- 

 meter. Each nerve when excited evoked electrical changes in the observed region, 

 the left one (on side of lesion) more than the right. On stimulating the columns of 

 the cord, and observing the effect on the left nerve, it was found that, with the 

 ordinary strength of stimulus, very slight effects of 4 and 8 followed excitation of the 

 posterior column of the same side, and no effects were obtained with this strength of 

 stimulus from either the lateral of the same side or the columns of the opposite side. 



On the other hand, in the right nerve, effects of 35 and 56 were evoked by 

 stimulation of the right posterior, and varied effects from 2 to 65 on stimulation of 

 the right lateral. 



The observation could not be repeated with stronger stimulus owing to the failure 

 of the animal. 



An examination of all these results and comparison with those of Sections 3 and 4, 

 will show that the effects aroused in the mixed nerve by stimulation of the spinal 

 cord must be mainly due to nerve impulses travelling from the cord down the afferent 

 (sensory) fibres ; since the effect due to impulses travelling down exclusively efferent 

 (motor) fibres, in the first place, is very small in amount and, in the second place, is only 

 produced by a strength of stimulus in excess of that employed in the experiments on 

 the mixed nerve, and finally, is then mainly evoked by stimulation of the lateral tract 

 of the same side as the nerve under observation. 



SECTION 6. THE INFLUENCE UPON THE ELECTRICAL EFFECT IN THE NERVE OF 



INTERVENING SECTIONS IN THE CORD. 



The experimental results to be studied under this heading throw more light upon 

 the relations of the sciatic nerves to the spinal cord. 



In the foregoing three groups of experiments, whilst excitatory electrical effects 

 were evoked in the afferent, efferent, and mixed nerves by stimulation of the 

 different columns in the cord, no direct evidence was afforded of the nature of the 

 path in the cord along which the impulses, starting from the excited cross section 



