3 l6 THE CAUSATION OF DISEASE. 



come from unlike individuals, there is a struggle of opposing 

 tendencies. 



Wherefore two important facts regarding man stand out 

 prominently, viz. : — 



1. That advantage accrues from change of E from time to 

 time. 



2. That advantage accrues from the marriage of unlike 

 individuals. 



The above considerations explain the good effects of " send- 

 ing a patient away." I have been accustomed to associate the 

 benefit derived from this course with the habit of primeval 

 man to wander about from place to place. Our ancestors 

 were nomadic probably for many thousands of generations, 

 and the wandering instinct is even now strong among us, so 

 that the human organism is still more or less adapted to a 

 continual change of locality, and at times actually craves it. 

 But this explanation, though probably correct so far as it goes, 

 is only partial. That offered by Spencer and Darwin goes far 

 beyond it, for it approximates to an ultimate explanation — to an 

 explanation, i.e., which does not leave anything further to be 

 explained, cannot be rendered plainer, cannot be referred to 

 any more general principle. 



It is not only in respect of climate that " change " is 

 beneficial to man. Within proper limits it does good in many 

 ways. See what a potent influence it has upon the mind ! 

 Most people sooner or later find out for themselves that the 

 great secret of enjoyment lies in continual mental change — not 

 necessarily in change between very many things, but in, at all 

 events, change from one thing to something else.* Indeed, 

 the mind even more perhaps than the body craves for variety. 

 This is, at any rate, true of the cultured mind, though the 

 desired change is not necessarily change of scene. The man of 

 culture does not need to change his locality in order to get 

 mental variety : he has never-failing sources of mental diver- 

 sion in his library, in his acquaintances, in the world arouud 

 him. But although the mind can thus, as it were, create its 



* In reference to the subject of change as a necessary factor in mental pro- 

 cesses, see Bain's " Law of Kelativity :" Mental and Moral Science. Alexander 

 Bain, p. 83. 



