CHANGE IN EXPRESSION OF DISEASE 293 



particular kind of process. It is probable that some diseased 

 conditions which get different names are fundamentally the same ; 

 it is their expression only that changes in response to the conditions 

 of nurture and environment. 



The facts of what is often called " transmutation of disease " 

 suggest that what is inherited is sometimes a very general 

 peculiarity, which finds this or that expression in relation to the 

 conditions of the body — a very variable soil — and according to 

 the liberating stimuli which are available, such as the diet, 

 climate, and other conditions of life. 



It is well known in medicine that a predisposition or diathesis 

 may express itself in half a dozen different ways — being poly- 

 morphic, as it is said — though there may be one way or two ways 

 which, being most frequent, may be called " diagnostic " or " dis- 

 tinctive." Thus, the tubercular tendency has several different 

 ways of expressing itself, probably depending mainly on the nature 

 of the nutritive and other environmental influences. 



But if the same disease may find different expression in, let 

 us say, three brothers, it is not surprising that the disease of 

 a parent may take a different, though analogous, form in the 

 offspring, and perhaps a third form in the grandchildren. It may 

 be intensified, or weakened, or directed on new lines, the change 

 depending, so far as we can see, partly on the amphimixis or 

 duality of the inheritance, and partly on the external conditions. 

 Thus, if both parents have a markedly phthisical tendency, the 

 probability is that there will be in the offspring a more pronounced 

 similar predisposition than if one of the parents had belonged 

 to an untainted stock ; or, again, apart from amphimixis, a 

 thorough change in habits and surroundings may at least greatly 

 inhibit the phthisical outcrop in the offspring. 



There is probably a very simple reason why a hereditary ten- 

 dency to nervous disease should have different expressions in 

 successive generations, and it is this : that many if not most 

 abnormal neuroses — e.g. epilepsy and insanity— emerge during 



