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Regarding the diseases of the chylo-poietic system as a 

 whole there is scarcely one of them to which heredity can- 

 not be said to have predisposed. Of course the influences 

 of life and circumstances have to be estimated in every case 

 as factors in the production or development of disease ; but 

 I maintain that in almost every case there is a pre-existing 

 disposition which has been inherited, and which acts as the 

 source from which morbid processes spring, or as the 

 foundation on which they are laid. To quote an-illustration 

 already given, why should several individuals exposed to the 

 same noxious influence say a chill be so differently 

 affected ? One will have as a consequence an attack of 

 influenza or bronchial catarrh, another sore-throat, another 

 rheumatism, another bronchitis or pneumonia, another lum- 

 bago, and so on. Why are some individuals so prone to 

 attacks of erysipelas, biliousness, sick-headache, etc. ? 

 Because they differ from each other as individuals in power 

 of resistance ; because of pathological habit ; but principally 

 because of constitutional predisposition which in nine cases 

 out of ten, will be found to rest upon a basis of heredity. 

 Their fathers or mothers may be found free from any such 

 affection as the children respectively suffer from ; but this is 

 not enough to prove their non-hereditary origin. We must 

 enlarge the cycle of heredity and inquire further back in the 

 pedigree, and if this inquiry also gives a negative reply we 

 must remember that hereditary diseases are somehow 

 mysteriously related to each other, and may in many in- 

 stances be found vicarious; thus it is possible that the father 

 may suffer from haemorrhoids, and the son from dropsy ; or 

 the first from gout and the latter from stone ; but still in 

 these cases the dropsy as well as the stone must be con- 

 sidered as hereditary. 



