ME THODS OF EX A MINA TION. 257 



should be undertaken. To avoid risk of contamination 

 with the smegma bacillus the meatus of the urethra should 

 be cleansed and the urine first passed should be rejected, 

 or the urine may be drawn off with a sterile catheter. As 

 stated above it is only exceptionally that difficulty will arise 

 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 ; 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 

 unnecessary. 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 five 

 or six weeks, to inoculate tubes of solidified blood serum, 

 under strict aseptic precautions, with portions of a tuber- 

 cular organ, e.g., the spleen. 



