50 EVOLUTION OF THE INFECTIOUS DISEASES 



severe disturbances which, if there is no timely intervention, 

 may result fatally. Between these two extremes we may 

 imagine an infinite variety of pathologic manifestations and 

 local or general immunizations. As we have indicated above, 

 acquired immunity will always be inversely proportional to 

 the severity of the attack. 



But in this short discussion which has at the moment no 

 other object than to present in a certain order and to corre- 

 late a total of experimental and clinical facts most of which 

 result from the memorable researches of Roux and Yersin, 

 Behring and Kitasato, Vaillard, Ehrlich, L. Martin, Grancher, 

 Marfan and others: and to bring out the difference in the 

 evolution of diphtheria and most of the other infectious dis- 

 eases, we must dwell upon the exact significance of the 

 "incubation period" in pathologic states caused by antigens. 



We are accustomed to designate the time which intervenes 

 between contagion and the appearance of the first symptoms 

 or, in other words the onset of disease, as the "period of 

 incubation." The studies of Ch. Richet, Hamburger and 

 Moro, Krauss, Besredka and Mile. Harde, Vaughan, Jobling 

 and others have shown that in the great majority of infectious 

 diseases as well as in pathologic states caused by previous 

 injections of heterologous albumins, of antigens, the " period 

 of disease" coincides almost exactly with the appearance of 

 specific antibodies in excess in the blood and we have been 

 able to establish that the symptomatology of all these patho- 

 logic states is determined by the nature and the site of the 

 reaction between antibodies and antigens. 



We may thus characterize the "period of incubation" by 

 reactions of antigens with normal antibodies; and the "period 

 of disease" by the reaction of antigens with antibodies in 

 excess. 



But if we admit these distinctions and this seems neces- 

 sary, we assume that in diphtheria and in the diseases analo- 

 gous by the nature and action of their antigens (tetanus and 

 botulism), the pathological manifestations appear during 

 the "period of incubation" while the "period of disease" is 

 concerned with recovery; all of which is contrary to w r hat 

 happens in the great majority of infectious diseases and in 



