RESISTANCE TO INFECTIOUS DISEASE 17 



the acute infectious diseases of which one attack protects from a sub- 

 sequent attack of the same disease. 



It may conduce to clearness if we should enumerate the factors that 

 have been described and assigned on the one hand to natural resistance, 

 and on the other hand to acquired resistance or immunity. We can 

 tabulate the factors in the following manner: 



Natural ob Physiological Inceeased Natural or Physiological 



Resistance Resistance 



C complement. 



. , . intermediary body. . , 

 Alexin J . Alexin « 



1 opsonin. 



[ agglutinin. 



complement, probably increased. 



intermediary body. 



opsonin. 



agglutinin. 



Phagocyte. Phagocyte — increased ( hyperleucocytosis ) . 



Acquired Immunity 



Complement — probably increased. 



Intermediary body — specific one produced. 



Opsonin — specific, stabile one produced. 



Agglutinin — specific one produced. 



("for exotoxin ~) 

 Antitoxin j for endotoxin | produced. 



Phagocyte — often increased but qualitatively unchanged. 



This tabulation exhibits the distinction between the physical basis 

 of physiological resistance and of the state of immunity. There is 

 another difference between them; any increase that can be called out 

 beyond the mean of physiological resistance is accomplished in a few 

 hours; and having been called out to meet a particular condition of 

 need of the body and the effect having been exerted, it passes off very 

 soon. It is rare that the effect of a hyperleucocytosis can be detected 

 for more than three or four days after it has appeared. The develop- 

 ment of the state of immunity, on the other hand, is a slow process 

 relatively and depends upon the setting into motion of certain cell- 

 functions, through which new substances are produced, which, being 

 first retained within the cells producing them, eventually are passed 

 into the blood. Hence it is that these new substances can be detected at 

 an earlier period of the infection in the spleen than in the blood. But 

 once they have been produced, the substances endure either for an 

 indefinite period, or the capacity to produce new ones of the same sort 

 is retained by the organism often for years. The blood may grow weak 

 in the typhoid immunity principle in the course of years following an 

 attack of typhoid fever, or a rabbit immunized with typhoid bacilli may 

 show after a time a great diminution of the blood agglutinins for 

 typhoid bacilli ; but the typhoid immunity persists in the one, as in the 

 other minimal quantities of typhoid bacilli will bring out, and without 

 the original delay, a new production of agglutinin that will restore the 

 lost amount! 



VOL. LXXV. — 2. 



