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others again, notwithstanding the employment of all sorts of 

 therapeutical and hygienic measures, are subject to continued 

 and repeated attacks (Lebert). Thus, again, with typhoid 

 fever, the poison of which, as established by Budd, is 

 propagated continuously, and never originates autochthon- 

 ously, and which can only germinate in a suitable soil. Such 

 disease germs pass into each one of us every day of our 

 lives ; why, then, do they not manifest their specific effects ? 

 And why, even when they do germinate, does the product 

 vary? Because, in the first instance, they must become 

 implanted in a suitable soil, or they produce no effect, and 

 secondly, because when they do germinate the product 

 varies with the soil. Thus while some may be peculiarly 

 predisposed to the action of some of those specific germs, 

 others will be found more or less insusceptible, and that 

 this predisposition or insusceptibility frequently amounts to a 

 -constitutional peculiarity, in the production of which heredity 

 has had a share, it is only fair to assume. As regards the 

 differentiation of individuals in relation to the respective 

 tissue-peculiarities which they have inherited and acquired, 

 I cannot do better than again quote the words of Sir James 

 Paget, who says : " This living soil is in each as personal 

 and distinct as any other constituent of personal character, 

 and the study of it must be intimately personal, with an 

 exact analysis of every disposition to disease." How this 

 predisposition or insusceptibility is produced, or in what it 

 consists we do not know ; we can only accept the facts ; but 

 giving full force to every possible factor of an external kind, 

 and, in the cases of insusceptibility, to the comparative 

 immunity produced by previous or primary attacks, 

 there still remains a far greater amount of evidence as 

 to the efficacy of individual predisposition and insuscepti- 



