USE OF ANIMALS 165 



of bacteria which are quite distinct but which in their mor- 

 phological and cultural characters are very similar, such as 

 is found in anthrax and anthrax-like bacteria. By injecting 

 these into the proper animals it is possible to distinguish the 

 one from the other by means of the pathogenesis. 



5. To produce antitoxin. To produce antitoxin, bacterici- 

 dal or agglutinating sera, animals are necessary. In the pro- 

 duction of the antitoxins used in medicine the larger animals, 

 of course, are employed; but for much of the experimental 

 work smaller animals are used. 



6. To test the antitoxic strength of sera. The experimen- 

 tal animals, largely guinea pigs, are the reagents for testing 

 the strength of toxins and the therapeutic value of the anti- 

 toxins. They are also used for testing tuberculin and mallein. 



7. For purposes of demonstration and in teaching. It is 

 necessary in demonstrating the various properties of bacteria 

 to use animals for purpose of instruction. 



While it is unfortunate that it is necessary to employ 

 animals in bacteriological investigation, there is at the present 

 time no other means by which the very important results for 

 both man and dumb creation can be obtained. 



Methods of inoculating animals. The methods of inocu- 

 lating animals vary according to the different facts about 

 which definite knowledge is desired. 



1. Cutaneous. This consists in rubbing the culture or the 

 substance containing the virus into the abraded skin. 



2. Subcutaneous. The bacteria are injected by means of 

 a hypodermic needle or by placing them in a pocket in the con- 

 nective tissue under the skin. When cultures are used they 

 are either injected under the skin with a hypodermic syringe 

 or placed under the skin by means of the platinum loop. When 

 infected material, such as glandered tissue, is used it may be 

 crushed, ground up in sterile salt solution or bouillon and in- 

 jected with a hypodermic syringe or a piece of the tissue may 

 be placed under the skin and held there by means of a suture. 



3. Intravenous. The bacteria are injected by means of a 

 hypodermic needle into a vein. In case rabbits are employed 



