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affects the inheritance of disease viz., that which has been 

 denominated "the tendency to reversion from all variations 

 of specific characters ;" for, as the preservation of the specific 

 characters of the species essentially concerns the law of 

 heredity, the determination of individual characters is mani- 

 fested most in the law of variation : and thus, the inheritance 

 of a disease-tendency, however probable, is not invariable, 

 as disease-tendencies, like parental characters of mind and 

 body, are either held in check or actually neutralised by one 

 of the parents of the child being healthy, so that the con- 

 stitutional disease of the other may be, in a manner diluted. 

 "Phthisis," says Dr. Maudsley, " is a notorious instance, 

 passing so directly from parent to child, as to entail the ex- 

 tinction of a family when it is not neutralised by favourable 

 inter-breeding. For such neutralisation, not of phthisis only, 

 but of other disease-tendencies, may undoubtedly be effected, 

 although we have not at present any knowledge of the laws 

 by which the good result is brought about ; the fact, how- 

 ever, is certain, and profoundly significant. The union of 

 two individuals, one of whom has a marked disease-tendency 

 of a particular kind, produces an organic constitution in 

 which it is held in neutralisation or check, never showing 

 itself in their children. It has become a disease-immunity 

 for that generation. Did we know the exact nature of the 

 neutralising process it would no doubt be possible, by suit- 

 able arrangements for subsequent breeding, to get rid entirely 

 of the morbid tendency and to obtain a perfectly sound stodk. 

 Unfortunately we do not, and so are liable to find the neu- 

 tralisation temporary, since it not unfrequently happens that 

 the union of the offspring which is apparently free from the 

 disease-tendency, because it is held in check, with a person 

 is also apparently free from it, produces an organic 



