238 TUBERCULOSIS. 



Methods of Examination. (i) Microscopic examination. 

 Tuberculosis is one of the comparatively few diseases in 

 which a diagnosis can usually be definitely made by micro- 

 scopic examination alone. In the case of sputum, one of 

 the yellowish fragments which are often present ought to be 

 selected ; dried films are then prepared in the usual way 

 and stained by the Ziehl-Neelsen method (p. 102). In the 

 case of urine or other fluids a deposit should first be 

 obtained by centrifugalising a quantity in a test-tube, or by 

 allowing the fluids to stand in a tall glass vessel (an ordinary 

 burette is very convenient). Film preparations are then 

 made with the deposit and treated as before. 



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

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

 subcutaneously ; if a 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 fluid is then 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 the tubercular 

 organs, e.g., the spleen. 



