266 TUBERCULOSIS 



to the experienced observer from this cause. (For points to be 

 attended to, vide p. 255.) 



(2) Inoculation. The guinea-pig is the most suitable 

 animal. If the material to be tested is a fluid it is injected 

 subcutaneously or into the peritoneum ; if solid or semi-solid it 

 is placed in a small pocket in the skin, or it may be thoroughly 

 broken up in sterile water or other fluid and the emulsion 

 injected. By this method, material in which no tubercle bacilli 

 can be found microscopically may sometimes be shown to be 

 tubercular. 



(3) Cultivation. Owing to the difficulties this is usually 

 quite impracticable as a means of diagnosis, and it is also un- 

 necessary. The best method to obtain pure cultures is to 

 produce tuberculosis in a guinea-pig by inoculation with tubercular 

 material, and then, killing the animal after four or five weeks, 

 to inoculate tubes of solidified blood serum, under strict aseptic 

 precautions, with portions of a tubercular organ, e.g. the spleen. 

 The portions of tissue should be fairly large, and should be well 

 rubbed into the broken surface of the medium. 



