CHAPTER XIY. 



THE USE OF ANIMALS FOR DIAGNOSTIC AND TEST 

 PURPOSES. 



SUITABLE animals are necessarily employed for many 

 bacteriological purposes. Thus they may be used as a 

 soil for bacterial growth, when, as in the case of tubercle 

 bacilli, the bacteria will not develop in the dead culture 

 media. For this reason material suspected to contain 

 tubercle bacilli is injected into rabbits or guinea-pigs, 

 with the knowledge that, if present, although in too 

 small numbers to be detected by microscopical or cul- 

 ture methods, they will develop their lesions in the 

 animal's bodies, and thus reveal themselves. The same 

 may be true of glanders and anthrax bacilli and of 

 other bacteria. Again, animals are used to test the 

 virulence of organisms, where, as in the case of diph- 

 theria, we have very virulent, attenuated, and non- 

 virulent bacilli of, so far as we know, identical cultural 

 characteristics. Here the injection of a susceptible 

 animal, such as the guinea-pig, is the only way that we 

 can differentiate between those capable of producing 

 diseases from those that are harmless. Still another 

 use of animals is to differentiate between two virulent 

 organisms, which, though entirely different in their 

 specific disease-poisons, are yet so closely allied mor- 

 phologically and in culture characteristics that they 

 cannot always be separated except by studying their 



