132 LABORATORY BACTERIOLOGY 



III 



ANIMAL INOCULATION FOR PURPOSES OF DIAGNOSIS 



It is not always possible by the ordinary culture methods to suc- 

 cessfully determine the specific nature of a disease from a small 

 piece of affected organ or tissue of the diseased animal or man. In 

 making a positive diagnosis, therefore, it is often necessary to resort 

 to animal inoculation. This is done by injecting into the animal 

 chosen a small quantity of the tissue or fluid supposed to contain 

 the virus of the specific disease, such as tuberculosis, glanders, 

 rabies, and often of swine plague, hog cholera, anthrax, diphtheria, 

 and others. Animal inoculation is fiirther demandatory in determin- 

 ing the degree of virulence of pathogenic bacteria, the strength of 

 toxins, antitoxins, etc. In other words, the living animal must for 

 the present serve in certain instances as a testing reagent. The fact 

 should be kept in mind that the lesions produced in the experimental 

 animal are not necessarily and in most cases they are not the same 

 as those in the animal (or man) from which the virus was obtained. 

 It is the rule, however, that each virus produces characteristic 

 lesions from which the disease can usually be diagnosed in the 

 smaller animal. 



Animals Used. — For simple diagnostic work the guinea pig and 

 rabbit are usually employed, although white and gray mice, dogs, and 

 other animals are sometimes used. 



Method. — In preparing the animal for inoculation the hair should 

 be removed over the area of operation by the use of scissors, and the 

 skin washed and disinfected. A solution of corrosive sublimate, 

 I to 1000, or a 5% solution of carbolic acid, may be used. The 

 incision should be made with a sharp knife. Liquid material is 

 usually injected with a hypodermic syringe. An anaesthetic should 

 be given whenever the pain inflicted is to be long continued or 

 excessively severe. The place of inoculation should be chosen 

 where a local swelling, infiltration of tissue, or abscess would not 

 interfere with the animal's locomotion. 



