CHAPTER X 



immunity 

 Phagocytosis and Humoral Immunity 



Early ideas of Pasteur on immunity — Opposition to the phagocytic 



doctrine — Cellular and humoral immunity. 

 Antigens and Antibodies— Complement — The two substances : Bordet's 



experiments. 

 Phagocytosis a fact capable of direct observation — Ferments of the 



leucocytes — Analogies with the digestive ferments. 

 Pfeiffer's phenomenon — Opsonins and bacteriotropins — Antibodies not 



an exact measure of the immunity. 



It is not necessary to have studied medicine or science 

 in order to ask oneself what is this immunity which appears in 

 infectious disease. Certain bacteria are pathogenic for certain 

 animal species and not for others ; the guinea-pig, for example, 

 does not take fowl-cholera and the fowl does not take anthrax. 

 Among people living in one family under the same conditions 

 and among soldiers in the same barracks living under the 

 same rules we see disease attacking some while others remain 

 free. Finally it is a popular conviction that anthrax does 

 not occur twice and that, as a rule, once an individual has 

 had measles or small-pox he never takes it again : these 

 are everyday examples of acquired immunity. 



" Immunity against infectious diseases ought to be 

 understood to mean the sum total of all the phenomena 

 to which is due the resistance of an animal body to the 

 microbes which produce these diseases '' (Metchnikoff). 

 Immunity may be innate or acquired. Natural acquired 



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