396 



MESSRS. F. GOTCH AND V. HORSLEY 



along fibres which do not pass out of these columns, and a strict localisation of nerve 

 impulses is with this intensity of stimulus possible. 



The posterior columns are particularly susceptible to injury, since they are especially 

 exposed to danger of drying, &c., in the preparation of the cord. This circumstance 

 must be always kept in view when experiments involving an intervening exposure of 

 the cord are made. We were much puzzled by the result of two experiments in 

 which, after dividing the cord in the dorsal and lumbar regions, we had exposed a 

 portion of the experimental tract in the intervening part, about the 12th dorsal, for 

 subsequent operative lesion. The following results were obtained : 



In these cases therefore all lateral column effects average with minimal stimulus 

 111, with maximal 166; whilst all posterior column effects average with minimal 

 stimulus 70, with maximal 145. It is seen that these results are exceptions to the 

 general rule (see p. 385) of the effect from the posterior being in the Cat larger than 

 that from the lateral. That this was really due to the prolonged exposure at the 

 12th dorsal injuriously affecting the posterior columns is shown by the fact that such 

 exceptional results were only obtained when an intervening portion had been thus 

 exposed. If prolonged exposure is avoided by performing the necessary operation 

 mmediately before the desired intervening lesions are to be made no such lowering 

 of the amount of the posterior column effect is observed. In this relation it is 

 possible to explain the comparatively small posterior column effect (see p. 385) of the 

 Monkey as in some measure due to a loss of excitability in these columns, which 

 seem to be much more susceptible than the laterals (CHAUVEAU). 



Influence of Section of one Posterior Column. It is possible to interrupt one 

 column only, and thus to obtain conclusive evidence of the extent to which the 



