iv] /'osftmfni/ or Sfiixort/ Area 109 



bo expected to occasion an isolated affection of sensory cortex I settled upon Tabes Dorsalis, 

 and an examination of the brain in three instances of this disease lias disclosed changes 

 limited to the postcentral gyms, and very similar to those I have described as the result of 

 old-standing lesions in the internal capsule. The discovery of such changes in Tabes Dorsalis 

 is, in my opinion, of the greatest possible significance, and one of the strongest points which 

 can be advanced in favour of the view I am advocating. 



In the brains of individuals disabled by amputation of one or other extremity reactive 

 alterations have also been found in the postcentral gyms, and these correspond in point of 

 level with those which I have previously described in the precentral or motor area. The 

 alteration resulting from amputation is not so marked as that seen in Tabes, or as that 

 resulting from a capsular lesion, and, so far as I can judge, consists of a reduction in 

 number of large pyramidal cells without much concomitant general distortion of the cell 

 lamination. 



In cases of capsular lesion, in Tabes Dorsalis and after amputations, the resulting changes 

 appear to concentrate themselves on the anterior or Rolandic side of the postcentral convolution, 

 and if any change does occur in the parietal cortex behind, it is of a kind which cannot 

 be displayed by the methods of histological research at command. 



The value of previously collected clinico-pathological and experimental observations has 

 suffered depreciation owing to the preexisting erroneous and confusing supposition that the 

 postcentral gyrus formed part of the motor area, and all data will have to be subjected to 

 revision. In 'the study of future cases observers will have to be specially cautious in satisfying 

 themselves that the lesion on which they base their conclusions is limited in extent to the 

 postcentral gyms. Everything considered, there seems to be nothing in recorded cases which 

 can be used to overthrow the view that this gyrus is a sensory centre. 



In regard to Ferrier and Horsley and Schafer's statement that the gyrus f'ornicatus is 

 a sensory centre, it will be shown in a later chapter that histological study lends no colour 

 to such an assumption, and I can only think that in the operation which they practised, 

 removal of that gyms, they injured the fibres of the "cortical lemniscus" on its way to the 

 1 it ist central convolution. 



The separate localisation of the various components combining to produce "common 

 sensation" is beset with difficulties. However, the view is promulgated here that the post- 

 central area, like better-known sensory realms, is divisible into a purely sensory part, to 

 which all impressions primarily pass, and an investing psychic part. The former occupies 

 the postcentral area proper and, in accordance with my thesis, its destruction should lead 

 to abolition of psychic, as well as impairment of fundamental sensory components; the latter 

 covers the intermediate postcentral field and may extend further back in the parietal direction; 

 its destruction should lead to isolated disturbance of psychic sensory attributes. Some clinical 

 and pathological findings substantiate this view. The fact that fundamental attributes, such 

 as the simple recognition of touch, pain, heat, and cold, are only dulled and rarely or never 

 abolished in cases of cortical lesions, is probably due to the participation of subcortical inter- 

 mediate stations in the receptive act. 



