THE CAUSATION OF DISEASE. 2/9 



generations before lie can get it to vary at all. A hidden 

 silent change meanwhile goes on, the tendency to obviously 

 vary increasing : the numerical value of S rises from I to I o. 

 ■' We have good grounds," says Darwin,* " for believing that 

 the influence of changed conditions accumulates, so that no 

 effect" (he evidently means here obvious effect) "is produced 

 on a species until it has been exposed during several genera- 

 tions to continued cultivation and domestication." 



Our case of insanity is therefore parallel with the variations 

 of wild plants under domestication. In both a peculiar E 

 operates during many generations, leading to a hidden specific 

 change, which finally breaks out into an obvious variation — • 

 physiological in the one case, pathological in the other. 



* Vol. II. "Animals under Domestication," p. 249. 



V 2 



