SENSORY CENTRES. 91 



ment, or the result of movement, in man or in an 

 animal, is an indication of activity in the central 

 nerve-system, and is probably due to the activity 

 of a certain part only, we find it convenient to 

 recognize this in our nomenclature. The term 

 nerve-centre is here used to imply a portion of 

 the nerve-mechanism, which can act more or less 

 independently of the rest, and which by its activity 

 produces certain, more or less definite motor or 

 other effects, observable and separable from those of 

 the rest of the central mass of the nerve-mechanism. 



This paragraph implies the belief that there are 

 nerve-centres, as above defined, existent in the 

 brain. Ferrier's experiments and numerous other 

 facts tend to support that view. 



In speaking of nerve-centres in the brain, we 

 do not here wish to express the belief that these 

 necessarily exist as localized anatomical areas of 

 brain tissue separate from the surrounding nerve- 

 mechanism, although this may be true. I think 

 that we have framed a definition without implying 

 such anatomical isolation as an essential fact. 



An hypothesis is useful, if it leads to systematic 

 experimentation and the record of observations, 

 and I trust to be able to show that certain pro- 

 positions may be defined and investigated by means 

 of this working hypothesis that nerve-centres do 

 exist as defined above. 



In Terrier's * experiments the sensory centres in 

 the brain were sought for by observing that move^ 

 ments, or absence of movement, indicating blindness 



* Op. cit., p. 165. 



