THE INHERITANCE OF DISEASE 499 



stitution also was often thought to be expressed in physical 

 characteristics. When functional characteristics were thought 

 of as directly related to disease the term "diathesis" was 

 frequently used. Thus people of a certain inherited "con- 

 stitution" were regarded as especially Hable to tuberculosis, 

 particularly to that of the lymphatic glands on the basis of 

 a "scrofulous diathesis." 



When ideas were crystalhzed during and after the classical 

 bacteriological studies of the latter quarter of the last 

 century the conception of the scrofulous diathesis was first 

 amphfied in an attempt to harmonize it with new observa- 

 tions, and then almost, if not quite discarded, as being at 

 best inadequately grounded. The considerations advanced 

 in amplification of the conception are of considerable interest 

 in the present connection. 



It was first shown that the lymphatic lesions characteris- 

 tically associated with the diathesis were tuberculous and 

 that they had in general the same etiology as pulmonary 

 tuberculosis. It was soon very evident that it was difficult, 

 if not impossible, to discriminate between those physical 

 characteristics that might be preexistent and possibly 

 reflect predisposing causes, and those that were the con- 

 sequences of long-continued chronic disease transmitted by 

 contact infection from generation to generation and often 

 persisting in the individual from earhest childhood to old 

 age. It also appeared that the other lesions, particularly those 

 of the skin, that had frequently been regarded as evidences 

 of a scrofulous diathesis were not tuberculous but were due 

 to casual infection with staphylococci, streptococci and 

 probably other microorganisms. 



This recognition of many of the appearances as "con- 

 sequences" greatly weakened the whole conception. The 

 further evidence that if there was a constitutional pre- 

 disposition it was not strictly specific for tuberculosis but 

 involved other inflammatory processes as well, put the 

 question out of touch with the progressive thought of the 

 time, which was primarily engaged in establishing specific 

 relationships, either of etiology or immunity. 



With the coincident and tremendous improvement in 

 hygienic conditions and nutritional well-being in Europe 



