468 



MESSRS. F. GOTCH AND V. HORSLEY 



The above experiment thus shows that with such an intensity of stimulus as that 

 used (1000) the result of an intervening hemisection on the same side as the nerve 

 is to abolish the nerve effect. If it is on the opposite side of the nerve, then the only 

 effect interfered with is that evoked by the stimulation of the posterior column on the 

 side of the lesion. It would therefore appear that with this strength of stimulus the 

 nerve impulses, which subsequently cause the electrical effects, are localised to one 

 side of the cord in both the area of stimulation and the subsequent path through the 

 cord from that area to the issuing nerves. 



There is, however, one point to which it is desirable to draw attention before 

 proceeding to the next experiments. This is the absence of any effect in the left 

 nerve when, with a hemisection limited to the left side, the right posterior column is 

 stimulated. We do not interpret this as implying that there is no crossed path from 

 the opposite posterior column to the roots of the lumbar nerves, but that either such 

 crossing has to a great extent occurred at a higher level than the 1st lumbar vertebra,, 

 the level of the section, or that the hemisection had either directly (by injury) ov 

 indirectly lowered the excitability of the neighbouring posterior column, and that 

 thus the intensity of stimulus used was inadequate to evoke nerve impulses which 

 could pass, down the afferent fibres of such an indirect path as connects this column 

 with the nerves on the opposite side. This latter supposition is rendered not improb- 

 able by an experiment made upon an animal (Cat, 283)* in which the hemisection had 

 been performed four months before the experiment. The cord of this animal was 

 exposed and divided for excitation at the 10th dorsal (the hemisection had been made 

 on the left side at the 12th dorsal). The electrical effects produced in the two nerves 

 by excitation of the different columns (coil 2000) were as follows : 



* For full description of this auimal during life and after death see pp. 429-430. 



