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ment of any individual may be modified also by suffering, 

 indulgence, moral control, or religious enthusiasm, and thus 

 the more we analyse the microcosm of man, the more we 

 -are astonished by the infinite and ever-increasing differen- 

 tiation of individuals. 



Idiosyncrasy is also a factor in predisposing to disease, 

 but may likewise become an agent in producing the very 

 -opposite condition viz., insusceptibility. Idiosyncrasies 

 are invariably congenital, and the term is never applied to 

 those peculiarities which have been acquired. There can 

 be no doubt that they depend upon peculiarities of physical 

 structure, however impotent we may be in seeking to 

 demonstrate their physical cause. As to their real nature 

 I regard them with Mr. Jonathan Hutchinson as " dia- 

 theses, or parts of diatheses, developed, intensified, and 

 .-specialised by hereditary transmission," as, in fact, "diathesis 

 brought to a point," and the very acme of individuality, for 

 how often do we see such constitutional peculiarities, in 

 certain individuals, so intensely developed as to render their 

 eccentricity especially striking, if not manifestly absurd? 

 The phenomena included under the term I am now discus- 

 sing are variously developed in different individuals, but 

 "whilst some of them may be neutralised, or otherwise 

 modified by age and circumstances, all are inherited 

 usually last during the whole period of life, more or less 

 and are almost invariably transmitted. Idiosyncrasies, like 

 the temperaments, do not necessarily entail any proclivity 

 to disease, but may variously predispose to certain morbid 

 processes, as, for example, the specific or exanthematous 

 fevers. In the case of one, such an extraordinary immunity 

 may be revealed that the specific virus may produce no 

 apparent effect ; whilst in that of another, such an incredible 



