PREFACE xiii 



variations in the environment of the cell as alter- 

 native explanations of modifications in the character 

 of nervous action caused by food or drugs, it is towards 

 the latter theory that the balance of probability 

 inclines. Even in the case of simple elements a 

 superabundance is not only sometimes useless, but 

 may be highly prejudicial. Phosphorus, for instance, 

 though a constituent of nervous matter, when given 

 in moderately large doses, far from contributing to 

 the building up of the tissues, rather increases the 

 katabolic tendency. The building up of our tissues 

 depends, one may say, less on the quantities of the 

 materials provided than on the play of those dynamic 

 influences whereby metabolism in the nervous system 

 and through it in the whole body is governed. 



Though the chemical processes of metabolism are 

 both varied and complicated in the highest degree, 

 yet in all of them certain physical factors, such as 

 the simple forces of attraction and repulsion, play, 

 there is reason to believe, an essential part. We may 

 note the influence of these forces in the contraction 

 and expansion of vaso-motor action, we may infer it 

 in other instances of physiological action also, and by 

 keeping it always in view we may hope to penetrate 

 the mysteries of some problems which, when con- 

 sidered without making due allowance for this factor, 

 must remain insoluble. 



In dealing with the subject of the functions of the 

 cerebellum too many pages have perhaps been given 

 up to the consideration of the anatomy of the spinal 



