THE INOCULATION OF ANIMALS. 237 



action in the animal body both without and under the 

 influence of specific serums upon them. In this way 

 the typhoid and colon bacilli may be separated, or the 

 pneumococcus and streptococcus. Still, a different use 

 of animals is to measure the protective effect of anti- 

 toxic and bactericidal serums; thus, diphtheria antitoxin 

 is added to diphtheria toxin and injected into guinea- 

 pigs, and streptococcus immunizing serum is mixed 

 with living streptococci and injected into the vein of 

 a rabbit. The use of animals to develop through bac- 

 terial injections protective serums will be dealt with 

 under the special bacteria by whose products they are 

 produced. 



THE INOCULATION OF ANIMALS. 



The inoculation of animals may be made either 

 through natural channels or through artificial ones: 



1. Cutaneous. Cultures are rubbed into the abraded 

 skin. 



2. Subcutaneous. The bacteria are injected by 

 means of a hypodermatic needle under the skin, or 

 are introduced by a platinum loop into a pocket made 

 by an incision. 



3. Intravenous. The bacteria are injected by means 

 of a hypodermatic needle into the vein. This is usually 

 carried out in the ear vein of the rabbit. If rabbits 

 are placed in a holder, so that the rabbit remains quiet 

 and only the head projects, it is usually easy to pass a 

 small needle directly into one of the ear veins, espe- 

 cially those running along their edges. If the ear is 

 first moistened with a 3 per cent, carbolic acid solution, 

 and then supported between the finger inside and the 



