96 The Post-central Gyrus in Cases of Amputation [CHAP. 



easy detection of the alteration about to be described was negatived because, as far as could be judged, it 

 was limited to the Rolandic wall and lip of the postcentral gyrus, and confined in its general distribution 

 to the postcentral area proper. 



Under a low power of the microscope the first points to strike one were the shallowness and pallor 

 of the cortex here and also the pallor of the immediately subjacent white substance, pointing to a loss in 

 fibre wealth ; further one noticed especially that the line of Baillarger, usually prominent, lacked distinctness. 

 Under a higher power of the microscope it seemed that the stress of affection had fallen on the line 

 just mentioned and on the radiations of Meynert. The latter bundles were deprived in great measure of 

 their large fibres and presented an attenuated as well as a sinuous appearance, like that seen in the cortex 

 in many other atrophic conditions. The large fibres characterising the interradiary field of the normal post- 

 central gyrus were also markedly deficient, but the finer plexus of fibres situated here, and the supraradiary 

 plexus were fairly well preserved. As the zonal layer is weakly developed in the healthy condition any changes 

 which might have been present in it did not attract attention. 



There was some difficulty in deciding whether all these changes were more pronounced in one situation 

 than in another, and it was only after examining many sections that I decided on making a statement to 

 the effect that the lower half of the field had suffered more than the upper. 



The interest in this case lies chiefly in the evidence it provides that interruption of the 

 sensory tract at the level of the internal capsule is attended by changes in the cortex of the 

 postcentral gyrus similar in nature and distribution to those found in Tabes Dorsalis, and I 

 record it because I think it increases the importance of the latter as an argumentative basis 

 in the question of sensory localisation. 



The fact that the sensory disturbance was incomplete in the leg, and that the upper 

 part of the precentral area suffered less in comparison with the lower is significant. 



The Postcentral Gyrus in Cases of Amputation. 



In making the observations which are now to be recorded some of those brains used for 

 the determination of points in the differential localisation of the motor area were again employed. 

 But, whereas in the case of the motor area one was guided by the occurrence of a positive 

 alteration ("reaction a distance") in cells still in existence, the conditions in the case of the 

 postcentral gyrus were negative. In discussing the reactive changes occurring in the dominant 

 cells of the motor neurones subsequent to section of the peripheral nerve, it was pointed out 

 that those alterations were slow in supervention, and that the delay was probably due to the 

 fact that the degenerating influence had to stem the stream of physiological conduction. But 

 in the case of the cortical sensory termini the conditions are reversed, and d priori we 

 would expect in spite of the interposition of stops in the sensory neuronic chain to be 

 mentioned hereafter that in them degenerative changes would manifest themselves more 

 rapidly and the resulting disintegrative process soon be accomplished. Hence, in an old- 

 standing case of amputation with signs of "reaction a distance" still persisting in the giant 

 cells of the motor area, we should find in the cortical platform pertaining to the severed 

 sensory nerve, not active change, but evidence of previous affection, betrayed by a disappearance 

 of a certain number of cell elements. This I firmly believe to be the case. But at the risk 

 of weakening the force of my argument I must now point out that, while a statement may 

 appear readily credible that a numerical deficiency in cells exists in a given part, it is not so 

 easy to supply direct proof of the correctness of such a statement, especially when the enumera- 

 tion concerns relatively small and closely-packed cells, like those in the postcentral gyrus ; nor is 



