CHAPTER IV 



METHODS FOR EFFECTING ACTIVE IMMUNIZATION OF 



ANIMALS 



IN overcoming an infection, acquired either naturally or artificially, 

 the macroorganism develops antibodies, or protective substances, 

 against the infecting agent. Possessed of these antibodies, the animal 

 can subsequently withstand a more severe attack of the same infection. 

 Thus, the body-cells of the animal itself are actively concerned in pro- 

 ducing these antibodies, and the resulting protection or immunity is 

 therefore called " active immunity." 



The general term "antigen" has been applied to any substance that 

 can stimulate the formation of an antibody. The immunity following 

 scarlet fever is an example of active acquired immunity, although the 

 antigen is unknown. In order to acquire immunity it is not always 

 necessary for a person to have had the disease. Thus, a severe infec- 

 tion with the antigen of typhoid fever Bacillus typhosus results in a 

 general reaction, exhibiting symptoms and course known clinically as 

 typhoid or enteric fever; whereas, if the antigen is attenuated and in- 

 jected artificially in small doses in the form of a vaccine, the body-cells 

 react, producing antibodies and a resulting immunity against typhoid 

 fever, without discomfort or danger to life. This process is known as 

 vaccination, the term being first applied to a similar procedure employed 

 in inducing an immunity against smallpox by the inoculation of a small 

 dose of the antigen attenuated or modified by passage through the cow 

 (cow-pox virus) . 



This process of stimulating the body-cells to produce antibodies is 

 called active immunization, and, while the immunity following disease 

 is an example, the term is generally applied to artificial immunization, 

 as in vaccination, which serves in medicine, therefore, the primary pur- 

 pose of effecting prophylaxis. In laboratories active immunization of 

 animals is generally undertaken with a view to obtaining serums to 

 be used for diagnostic or therapeutic purposes. 



Practically, any protein may serve as an antigen. Thus, animals 

 may be immunized not only with various bacteria, but with serum al- 

 bumins and globulins, milk, egg-albumen, epithelial cells, etc. It must 

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