XVII. EXPERIMENTAL INOCULATION OF 

 ANIMALS. 



The use of living animals for inoculation experiments 

 may become a necessary procedure in the Bacterio- 

 logical Laboratory for some one or more of the follow- 

 ing reasons : 



A. Determination of Pathogenetic Properties of Bac= 

 teria already Isolated in Pure Culture (see page 315). 



The exact study of the conditions influencing the 

 virulence (including its maintenance, exaltation and 

 attenuation) of an organism, and precise observations 

 upon the pathogenic effects produced by its entrance 

 into, and multiplication within the body tissues can 

 obviously only be carried out by means of experimental 

 inoculation; whilst many points relating to vitality, 

 longevity, etc., can be most readily elucidated by such 

 experiments. 



B. Isolation of Pathogenetic Bacteria. 



Certain highly parasitic bacteria (which grow with 

 difficulty upon the artificial media of the laboratory) 

 can only be isolated with considerable difficulty from 

 associated saprophytic bacteria when cultural methods 

 alone are employed ; but if the mixture of parasite and 

 saprophytes is injected into an animal susceptible to 

 the action of the former, the pathogenic organism can 

 readily be isolated from the tissues of the infected 

 animal. The pneumococcus for example occurs in 

 the sputum of patients suffering from acute lobar 

 pneumonia, but usually in association with various 

 saprophytes derived from the mouth and pharynx. 

 The optimum medium for the growth of the pneumo- 

 coccus, blood agar, is also an excellent pabulum for the 



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