253 HEREDITY AND DISEASE 



creature is inseparable from surroundings of some sort ; and we 

 must not object to the distinction between innate (or idiopathic) 

 diseases and acquired diseases because we know that the innate 

 disease must have an evocative environmental stimulus, and 

 that an acquired disease necessarily involves some organismal 

 susceptibility. 



What, then, is the distinction ? It is the old distinction between 

 a variation and a modification. An innate disease presupposes 

 some germinal variation to start with, some germinal peculiarity 

 to continue with. It is there, whether it finds expression or not. 

 If it does not find any appropriate nurture, it will not express 

 itself in development, but neither will the normal process of 

 thinking find expression without the appropriate liberating 

 stimuli. If an indispensable process, the structural rudiment 

 of which is a component part of the normal inheritance, finds no 

 nurture, the organism of course dies. If a dispensable process, 

 such as an innate disease — the structural rudiment of which 

 is also part of the inheritance — finds no nurture, the organism 

 may of course survive if otherwise normal ; but the rudiment of 

 the disease may simply lie latent, and may be expressed in the 

 next generation. Eventually, whether it finds expression or 

 not, it may die away altogether, just as useful variations seem 

 sometimes to disappear. This might be called the racial cure 

 of disease. 



An acquired disease is exogenous, not endogenous, in origin. 

 It arises, apart from any particular innate predisposition, as the 

 direct result of inappropriate nurture (in the widest sense) ; 

 of unnatural function, over-function, or lack of function ; and 

 of intruding parasites — e.g. bacteria. 



But there are two complications — (i) An acquired disease 

 may operate in an organism which has an innate bias to disease 

 — e.g. when a tubercle bacillus infects a phthisical constitution. 

 (2) A diseased condition may be the result of premature or 

 local arrests of development, or of excess of development, or of 



