THE SPINAL CORD AND CEREBELLUM 141 



equilibrium is an essentially voluntary act, it follows 

 that the nervous mechanism by which it is carried 

 out must of necessity contain voluntary elements. 

 These, as Foster remarks* in the above passage, are 

 those which are chiefly lacking after the removal of 

 the cerebellum. We are, however, so much accustomed 

 to the sensory and the ' increase of impulse ' elements 

 in voluntary action that the liability to error in this 

 matter is very great. 



It has, moreover, been pointed out that, although the Secondary 



° centres of 



cerebellum undoubtedly contains cells, the property the eere- 

 of which, by reason of their size, must be to increase system, 

 the impulse of other cells, there are probably others 

 similar in function, though weaker in the degree of 

 the force they generate, to be found in the spinal 

 cord, as, for instance, in Clarke's column. The 

 existence of secondary ' increase of impulse ' centres 

 seems, indeed, not one whit less natural than of 

 secondary sensory or motor centres, and all may 

 probably be said to depend on the fact that the 

 nervous system is the result of fusion of separate 

 elements. The possible existence of several collec- 

 tions of ' increase of impulse ' or reinforcing cells is 

 a factor of great importance, and one which on many 

 occasions has been entirely overlooked. It gains 

 some support, moreover, from the fact that the lower 

 you descend in the animal scale, the less perceptible 

 are the evil results of extirpation of the cerebellum. 

 There does, therefore, appear to be some ground for 

 * Quotation, p. 122. 



