

TUBERCULOUS SPUTUM 393 



Fortunately, owing to the peculiar staining reaction of the tubercle 

 bacillus, the method is comparatively simple. 



If it is inconvenient to examine the sputum for a day or two a 

 little 1-20 carbolic should be added. This preserves the sputum, 

 and the tubercle bacilli retain their staining power for months. 



1. Sputum. Film specimens are prepared by smearing a little 

 of the sputum on to a slide with a needle so as to form a thin film 

 covering two -thirds of the surface, or by placing a particle of the 

 sputum on one slide, applying another slide, pressing together, 

 and then drawing apart so that a thin film is left on each slide. 

 The thick portion of the sputum should be used, the thin mucoid 

 portion being rejected. If the sputum is thin and watery, the 

 thicker portion can be obtained by covering the bottom of a 

 Petri dish with filter-paper, placing a large drop of the sputum 

 on this, amd working it over the paper with a bent steel needle. 

 The paper absorbs the water, leaving the thicker material on the 

 surface. If there are any small yellow caseous particles present 

 these should be chosen, and sufficient material should be used so 

 as to form a distinct but not too thick film ; a little experience 

 will soon decide the right amount ; too thin a film should be 

 avoided. The film is dried and fixed in the usual manner 

 (generally by heat), and then stained by one of the following 

 methods : 



(a) Ziehl-Neelsen method. The slides are stained by flooding 

 with filtered, undiluted carbol-fuchsin and warming for two to 

 five minutes on a piece of asbestos cardboard supported on a 

 tripod, or on a heated penny (p. 126), or the slides flooded with 

 the stain may be held in the forceps and carefully warmed over a 

 flame, or the preparations may be immersed in a dish of the stain, 

 covered, and placed in the warm incubator for half an hour. In 

 no case must the stain be allowed to boil, or the bacilli may lose 

 their staining power ; it should only be warmed sufficiently to 

 steam (50-60 C.), and as evaporation takes place more stain 

 (always filtered), or better, 5 per cent, carbolic, should be added. 

 After staining, the preparations are rinsed in water and are then 

 decolorised by treating with 25 per cent, sulphuric or 30 per cent, 

 nitric acid. The preparation may be flooded with the acid, but 

 a better method is to immerse the preparation in a jar (Fig. 22. 

 p. 125) containing the acid. In the acid the colour changes after 

 a few seconds to a yellowish brown, the preparation is then rinsed 



