122 THE CAUSATION OF DISEASE. 



mother from being inherited. That there are hidden principles 

 capable of such practical application, I doubt not ; but it would 

 need one endowed with the genius and thoroughness of a 

 Darwin to discover them, and, even if we could discover them, 

 they would be of little practical use, for how many young 

 marriageable folk would listen to our words of wisdom ? 



To sum up the chief points regarding reversion, so far as 

 they bear upon practical medicine : — 



1. Reversions to serious pathological states rarely occur, 

 because the graver forms of disease have no great ancestral age. 



2. Reversions to physiological states may occur under 

 certain conditions of E and as a result of particular crossings. 

 These may be physiological in the reverting individual, as in 

 the ancestor from whom they are derived ; or it may happen 

 that the physiological characters show a tendency to become 

 pathological in the reverting individual, through their imperfect 

 adaptation to modern environments ( = sub-pathological varia- 

 tions) ; or, finally, these originally physiological characters may 

 be distinctly pathological in the reverting individual, as in 

 persistent branchial clefts. 



3. The principle of reversion explains the vis medicatrix 

 natures. This is favoured by subjecting the individual to an 

 environment as like as possible to that of primitive man ; 

 or, by crossing an individual showing a disease-tendency 

 with one showing a character very unlike the pathological 

 one, on the principle that crossing of unlike individuals tends 

 to a reversion to the status quo ante the development of the 

 unlike points, namely, health. 



4. Most, if not all, diseases are attended by or rather, consist 

 in, a multitude of reversions, for, in so far as the structural 

 alterations of disease are partial dissolutions, they must in 

 some degree be reversions ; for a partial dissolution must 

 necessarily tend to disclose a tissue state belonging to a past 

 evolutionary era. 



