vi PREFACE 



degree of correspondence in regard to movement, for 

 in this wide world of ours there is no government 

 which does not rest upon a foundation of force, and 

 the transmission of force implies action or movement. 

 The reduction of chemical or physiological problems 

 to a physical basis is, moreover, in some respects a 

 process of simplification, and an endeavour to define 

 the character of the movements which take place in 

 the nerve -cells may be justified, if but partially 

 successful, by the hope that it may ultimately lead 

 to more direct and thorough methods of controlling 

 them. 



It is surprising to observe to what extent the 

 physical or dynamic factor lies apparently at the root 

 of some of the commonest and yet most important 

 processes in medical practice. Indeed, to take a 

 striking instance, it will probably have to be acknow- 

 ledged, in default of any other equally credible 

 explanation, that the immunity conferred by vaccina- 

 tion is, in reality, merely the result of a dynamic im- 

 pression produced upon the nervous system. This will 

 become to some extent apparent if we fully realize 

 the meaning of certain characteristics of the nervous 

 -system, and the consequences of its relations to the 

 whole organism. 



To illustrate this, let us take a case. When some 

 venturesome boy imprudently takes his first plunge 

 in the practice of smoking by consuming one of his 

 father's strong cigars, the result is usually such a 

 revolution in his interior as to make him regret his 



