John Hughlings Jackson, 



xxi 



animals. He, however, never accepted the doctrine of exclusive localisation, 

 holding that though each centre represents one set of movements in particular, 

 yet it represents all more or less. 



In the phenomena of disease Jackson always insisted on there being a 

 positive as well as a negative element. This is the central idea of his 

 explanation of the phenomena of insanity, post-epileptiform states, aphasia, 

 etc., and is founded on his views as to the evolution of the nervous system. 



These cannot be better given than in his own words : — 



" Beginning with evolution, and dealing only with the most conspicuous 

 parts of the process, I say of it that it is an ascending development in a 

 particular order. I make three statements which, although from different 

 standpoints, are about the very same thing. (1) Evolution is a passage 

 from the most to the least organised, that is to say, from the lowest, well 

 organised, centres up to the highest, least organised, centres ; putting this 

 otherwise, the progress is from centres comparatively well organised at birth 

 up to those, the highest centres, which are continually organising through 

 life. (2) Evolution is a passage from the most simple to the most complex ; 

 again, from the lowest to the highest centres. There is no inconsistency 

 whatever in speaking of centres being at the same time most complex and 

 least organised. Suppose a centre to consist of but two sensory and motor 

 elements; if the sensory and motor elements be well joined, so that 

 ' currents flow ' easily from the sensory into the motor elements, then that 

 centre, although a very simple one, is highly organised. On the other hand, 

 we can conceive a centre consisting of four sensory and four motor elements, 

 in which, however, the junctions between the sensory and motor elements 

 are so imperfect that the nerve currents meet with much resistance. Here 

 is a centre twice as complex as the one previously spoken of, but of which 

 we may say that it is only half as well organised. (3) Evolution is a passage 

 from the most automatic to the most voluntary. 



" The triple conclusion come to is that the highest centres, which are the 

 climax of nervous evolution, and which make up the ' organ of mind ' 

 (or physical basis of consciousness), are the least organised, the most complex, 

 and the most voluntary. So much for the positive process by which the 

 nervous system is ' put together ' — evolution. Xow for the negative process, 

 the ' taking to pieces ' — dissolution. 



" Dissolution being the reverse of the process of evolution just spoken of, 

 little need be said about it here. It is a process of undevelopment ; it is a 

 ' taking to pieces ' in the order from the least organised, from the most 

 complex and most voluntary, towards the most organised, most simple, and 

 most automatic. I have just used the word ' towards,' for if dissolution 

 were up to and inclusive of the most organised, etc., if, in other words, 

 dissolution were total, the result would be death. I say nothing of total 

 dissolution in these lectures. Dissolution being partial, the condition in 

 every case of it is duplex. The symptomatology of nervous diseases is a 

 double condition ; there is a negative and there is a positive element in 



