CHAPTER VII. 



IMMUNITY AND IMMUNIZING AGENTS. 



We speak of immunity from and susceptibility to disease, indicating 

 thereby a difference in individuals regarding their responsive behavior to the 

 factors, forces or influences which may cause or prevent disease manifesta- 

 tions. The subject is one of intense interest in the light of modern biological 

 and bacteriological investigations. It has within recent years received more 

 attention from biologists, physiologists and bacteriologists than any other 

 branch of science and some of the results obtained are in many respects 

 marvelous. The discoveries thus far made are the mere beginnings of future 

 preventive medicine, which will make it possible to establish a system of 

 medical practice of which the chief aim will be to prevent rather than to 

 cure disease. 



Several kinds of immunity are recognized which may be tabulated as 

 follows: 



Immunity 



Inherited 



Racial ] 

 (Phylogenetic) j 



As observed in the different orders, 

 families, genera and species of the 

 animal kingdom. 



Individual ' 



Induced 



Active 



As observed in different individuals of the 

 same species or variety. (Ontogenetic.) 



As observed in the sexes of the same 

 species or variety. 



' Due to naturally induced 

 infections with disease 

 which produce immunity 

 to subsequent attacks, 

 as diseases of childhood, 

 acclimatization, etc. 



Natural 



Artificial 



Due to use of modified 

 toxins, bacterins, and 

 direct inoculation with 

 disease germs. 



Passive Use of antitoxins and other disease preventives. 

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