CHAPTER XIII. 



THE USE OF ANIMALS IN BACTERIOLOGICAL EXAMINA- 

 TIONS AND INVESTIGATIONS. 



Experimental animals. In the laboratory for the study 

 of infectious diseases experimental animals constitute a very 

 important part of the essential reagents. By experimental 

 animals is meant in this connection guinea pigs, rabbits, white, 

 field and house mice, and pigeons. Other species, especially 

 the carnivora, are sometimes employed. The use of these 

 animals is rendered imperative because there are at present 

 no other means for determining certain facts relative to the 

 disease producing power of microorganisms other than the 

 actual test of the virus upon the animal body. It is important 

 to keep in mind, however, that because a certain species of bac- 

 teria proves fatal to a guinea pig, it can not be assumed that 

 it is pathogenic for other species of animals. The conclusion 

 can not be drawn that because one species of animals succumbs 

 to a given organism this organism will prove fatal to 

 other species of animals. Many errors relative to the identity 

 of certain diseases affecting man and the lower animals have 

 been made because the results of the inoculation of a given 

 animal with the bacteria from different sources have given 

 apparently identical results. This is illustrated in the case 

 of human and bovine tuberculosis in which guinea pigs being 

 equally susceptible to the virus from both sources led the 

 earlier workers in bacteriology to assume that tubercle bacteria 

 from cases of tuberculosis in man and in cattle were identical. 

 Animals are used in bacteriological work for a large number 

 of purposes. Some of the purposes for which their use is im- 

 perative are appended. 



I. As a culture medium a form of plate culture where 

 the specific organism will not grow outside of the living body 

 or when it is impossible to isolate the organism in an artificial 

 medium. Again, when certain pathogenic bacteria, such as 



