76 INFECTIOUS AND PARASITIC DISEASES. 



represent predisposing causes, for only when the fly 

 is entangled in the web does the spider attack its victim. 

 It will be observed that this conception of disease 

 does not undervalue the part that infectious agents play 

 as direct or exciting causes of disease, but it further 

 recognizes fully the preponderating influence of those 

 accessory, auxiliary, or predisposing causes without 

 which the animate agents cannot act. The analytical 

 chart here shown aims to elucidate graphically this 

 view. To be sure, all of the diverse elements represented 

 are not operative at the same time in any infectious 

 disease; but one or several always are, and these act in 

 combination with the infectious agents. 



Referrinoj to the chart, it will be seen that 



there are three sub-divisions to heredity, 

 viz., race, family, and individual. 



Our knowledge of race as influencing 

 Race. infection is of comparatively recent date. 



This knowledge, besides having an impor- 

 tant bearing upon etiology, is of historical interest in 

 explaining the errors of judgment which in the past led 

 to great crimes. In many notable epidemics the Jews 

 were singled out for persecution, because they escaped 

 the prevailing scourge, their immunity being ascribed 

 to a special knowledge of the epidemic disease. During 

 cholera epidemics, the relationship to drinking-water 

 which was recognized, they were accused of poisoning 

 wells, and the brutal ferocity of insensate mob- violence 



