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peculiarities which distinguish us from one another in health 

 should also tend to modify or intensify our relative proneness 

 to certain morbid affections, by the neutralisation or develop- 

 ment of the morbid susceptibilities or predispositions which 

 have been transmitted to us. The physical likeness trans- 

 mitted by parents to their children is never exact. This is 

 sufficiently evident in features, size, weight, and all that con- 

 cerns external conformation. But, as Sir James Paget says : 

 " If we could be exactly endoscopic, we should observe 

 equal variation within ; the same want of exact likeness in 

 liver and lung, and, I venture to say, in blood, and lymph, 

 and plasma, and whatever goes to make up the whole person, 

 healthy or diseased. The inheritance of likeness in disease, 

 or liabilities to disease, is indeed clear evidence of the trans- 

 mission of likeness in the very minutest part of structure and 

 composition. But the likeness is never perfect ; it may in 

 different persons deviate this way or that ; it may vary 

 towards disease, or back again towards the healthy type ; 

 but it is never perfect, and, in successive generations, its 

 degree of unlikeness may in some persons increase to a 

 great width of difference." We thus see that however perfect 

 the likeness transmitted from parents to their offspring, it is 

 never either organically or dynamically exact, and however 

 closely the partus may resemble the parens physically, men- 

 tally, or morally ; however closely the former may resemble 

 the latter with regard to temperament, idiosyncrasy, diathesis, 

 and hereditary predisposition, yet each child preserves its 

 own individuality, by reason of the differentiation produced 

 by natural variability, to which every organic being is sub- 

 jected, in addition to heredity. 



I have now to consider the pathological aspect of heredity 

 or the influence of the hereditary element in disease. Let 



