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guards against disease. So also are climate, temperature, 

 moisture of atmosphere, and impurity of air. On these, 

 however, I shall not now dwell, as strictly speaking, in 

 discussing the hereditary element in disease, I should have 

 limited my observations to hereditary predisposition alone ; 

 but as the whole subject is too often lost sight of, I may be 

 excused for the few remarks I have made on the aetal, 

 sexual, and acquired sub-divisions. Speaking of predis- 

 position, Dr. Armstrong says : " This tendency seems to 

 have performed a very conspicuous part of ancient pathology, 

 and is, in my opinion, by far too much neglected by 

 practitioners in the present day. . . . The doctrine of 

 predisposition is of the greatest importance in a preventive 

 point of view ; and if we take the whole of its sources and 

 trace them through society, we shall find, that in the 

 civilised world at least, scarcely an individual can be said to 

 be physically sound. We shall find in almost every person 

 that there is some latent fault, which may become disorder 

 or disease when such an occasional agent or cause is applied 

 as will disturb the body, either generally or locally." 

 Predisposition, in fact, consists in a peculiar state of the 

 physical and mental constitution of every individual, which 

 renders him specially liable to suffer injuriously from the 

 effects of certain morbific agents ; and when these latter are 

 of a " non-specific " type, predisposition will determine the 

 particular disease which it shall induce in each of several 

 individuals similarly exposed to it ; whilst, in the case of a 

 specific " agent or " morbid poison," it determines the 

 relative liability of several individuals similarly exposed to 

 it, to become the subjects of the particular diseases it is 

 capable of originating, and also influences the severity of its 

 attack. 1 Thus, let us suppose several persons equally 

 1 Dr. W. B. Carpenter. 



