xvi Introduction 



Another direction in which developmental studies may prove serviceable, is the determination 

 of the time at which other cortical elements, to wit the nerve cells, make their appearance ; 

 because, it seems reasonable to assume that these follow the same sequence as the nerve 

 fibres ; taking an instance, there is full likelihood that in the case of those animals which 

 at the time of birth are incapable of locomotion, man is of course one, sensory cells 

 develop in advance of motor cells, and in this way light might be thrown on at all 

 events one very vexed question. Probably on account of the fact that our methods for 

 the study of developmental cytology are as yet imperfect, practically no work has been 

 done on this subject. 



2. The Histological Study of the Brain in Conditions of Disease. 



There are two important methods under this heading by which cerebral localisation 

 can be, and has been forwarded ; one is by taking notice of the course and destination 

 of secondary degenerations, either of experimental production or arising in nature, and it 

 supplies a means for securing information concerning the various sensory areas and the 

 motor field, as well as certain subcortical association tracts. The second method, in my 

 opinion of greater value and insufficiently exploited, is based on the principle that division 

 of a nerve is followed, not only by central, but by peripheral changes, changes which are not 

 confined to the divided segment but affect all links and all stations in the neuronic chain 

 of which it may form a part. The principle of course embodies Wallerian degeneration and 

 Gudden's atrophy, and issues have already proved that the application of the method is 

 correct in foundation : thus, Bolton has successfully utilised cases of old-standing blindness 

 of peripheral origin in defining the exact limits of the visual area ; and in the present 

 work full advantage is being taken, for the first time, so far as I am aware, of the changes 

 which occur in the motor area, in cases of amputation of extremities, and, in what I believe 

 to be the sensory area, in cases of Tabes Dorsalis. As many years have elapsed since 

 Gudden published the accounts of his experiments on retrograde degeneration, and we have 

 been familiar with Wallerian degeneration and its effects on structures at the end of the 

 conduction stream for an even longer period, it is surprising that these teachings have not 

 been more frequently applied to cortical localisation, and it can only be imagined that 

 they have not been on account of imperfections in our knowledge of the topographic 

 distribution of the various types of cortical cell lamination and fibre arrangement, and 

 because in the vastness of the human cerebral surface observers have not known where 

 to start and look for reactive changes. 



In addition to the conditions mentioned, others which occur to one as being suitable 

 for investigation and which come in this category are cases of prolonged deafness, anosmia 

 and ageusia of peripheral origin 1 , and they would certainly have been made use of in 

 this research had they been available. Finally, the morbid histologist has at his disposal 

 the brains of individuals who have suffered from some disability of central origin, I refer 

 to cases of congenital mutism and deafness, as typical examples ; and there are many other 

 kindred conditions to be sought which must of necessity be associated with mal-develop- 

 ment, direct or indirect atrophy, or disintegration of cortical elements, and which would 

 afford profitable material, just as Amyotrophic Lateral Sclerosis a disease which may be 

 included in this class has proved serviceable in my hands (vide chapter on the motor area). 



1 For localisation of the sense of taste, about which our information is so meagre, an examination of the 

 hippocampal region and insula in cases of excision of the tongue is to be thought of. 



