TUBERCLE BACILLUS. 83 



the preparation, the better the result. If the material is too 

 thick or viscid, a drop of distilled water is placed on the 

 slide and the material gently spread in this. The film must 

 be dried in the air, and not in the flame. Drying in the flame 

 is more rapid, but it always spoils the specimen. If the film 

 is thin, it will dry rapidly. After it is thoroughly dry, it is 

 fixed in the flame. It should not be held in the flame, but 

 passed through it three or four times. This fixes the bacteria 

 on the slide by coagulating the albumin in them. The next 

 step is to stain the specimen. 



Several different kinds of forceps have been devised to 

 hold the slide or cover-glass, but the wire forceps (Stewart) 

 are the best. They hold the glass securely and prevent soil- 

 ing of the fingers or clothing by the stain. With the ordi- 

 nary bladed forceps the stain is drawn up between the blades 

 by capillary attraction, and then it is impossible to keep it 

 from staining the fingers. 



The film is covered well with the stain, which is allowed 

 to act for a few minutes. To facilitate staining, the stain 

 may be warmed slightly. Decant the stain and wash the slide 

 in water. Stain again if necessary. Dry in the air, first 

 removing the excess of water with a blotter, and mount in 

 Canada balsam. The specimen is ready to be examined. A 

 T l y inch oil-immersion lens should always be used if possible. 



TUBERCLE BACILLUS : Special stains and staining-methods 

 are necessary for the tubercle bacillus. Many different 

 methods have been devised. The principle of them all is to 

 use a stain which stains so intensely that it cannot be removed 

 from the bacillus with either mineral acids or alcohol. The 

 tubercle bacillus is extremely resistant to decolorizing agents. 

 The film is prepared in the same manner as for the ordinary 

 bacteria. If the slide is made from sputum, the little white 

 or yellowish nodules should be selected, as they are most apt 

 to contain the tubercle bacillus. By shaking the sputum 

 with a 5 per cent, solution of carbolic acid little albuminous 

 masses are formed. One of these may be selected and spread 

 on the slide as thinly as possible ; or the mass is opened and 

 only its centre placed on the slide. The utmost care is neces- 

 sary in the handling of tubercular matter or any matter 



