METHODS OF EXAMINATION - 295 



Methods of Examination. (1) Microscopic Examinatioii. 

 Tuberculosis is one of the comparatively few diseases in which 

 a diagnosis can usually be definitely made by microscopic 

 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 stain (p. 108). 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 prepara- 

 tions are then made with the deposit and treated as before. If 

 a negative result is obtained in a suspected case, repeated exam- 

 ination 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. 

 280). The detection of tubercle bacilli by microscopical methods 

 in sputum, pus, faeces, and even tissues, has been greatly facilitated 

 by the recent introduction of a preparation called "antiformin." 

 This is a mixture of equal parts of liquor soda3 chlorinatae (B.P.) 

 and of a 15 per cent, solution of caustic soda. It has a re- 

 markable disintegrative and dissolving action on the tissues, etc., 

 so that after it has been allowed to act on sputum, for example, 

 and the mixture is centrifugalised, the resulting deposit is scanty 

 and the tubercle bacilli, if present, are accordingly greatly 

 concentrated. The time necessary may be judged of by the 

 appearance of the mixture, but it will generally be found that 

 the desired result will be obtained if one part of antiformin be 

 added to five or six parts of sputum and allowed to act for two or 

 three hours. 



(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 

 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 four or 



