CHAPTER XXI. 



ANIMAL INOCULATION. 



Animal inoculation has been referred to (1) as a method 

 of assisting in the preparation of pure cultures of patho- 

 genic organisms; (2) as a means of testing the poisonous 

 properties of substances produced in bacterial cultures; (3) 

 in order to test the ability of an organism to cause a disease; 



(4) for the production of various antibodies; it may be added 



(5) that some bacteria produce in the smaller experimental 

 animals lesions which do not occur in animals naturally 

 infected, but which nevertheless are characteristic for the 

 given organism. The best illustration is the testicular reac- 

 tion of young male guinea-pigs to intraperitoneal injections 

 of glanders bacilli. Experimental animals are also inocu- 

 lated (6) to test the potency of various bacterial and other 

 biological products, as toxins, antitoxins, etc. 



Guinea-pigs are the most widely used experimental ani- 

 mals because they are easily kept and are susceptible to 

 so many diseases on artificial inoculation. Rabbits are used 

 very largely also, as are white mice. For special purposes 

 white rats, pigeons, goats and swine are necessary. For 

 commercial products, horses (antitoxins) and cattle (small- 

 pox vaccine) are employed. In the study of many human 

 diseases the higher monkeys and even the anthropoid apes 

 are necessary, since none of the lower animals are susceptible. 



The commonest method of animal inoculation is undoubt- 

 edly the subcutaneous. This is accomplished most readily 

 with the hypodermic needle. The skin at the point selected 

 (usually in guinea-pigs the lateral posterior half of the 

 abdominal surface, in mice the back near the root of the 

 tail) is pinched up to avoid entering the muscles and the 

 needle quickly inserted. Clipping the hairs and washing 

 with an antiseptic solution should precede the inoculation 

 as routine practice. Frequently a small "skin pocket" is 

 all that is needed. The hair is clipped off, the skin pinched 

 up with small forceps and a slight snip with sharp scissors 

 is made. The material may be inserted into this pocket 

 with a heavy platinum needle. Cutaneous inoculation is 

 (224) 



