48 BACTERIOLOGY 



tion, and may be spread in a thin film on the cover-glass with the 

 platinum wire, which is sterilized in the flame before and after 

 using. The selection of the little white particles will be faciliated 

 if the sputum be poured into a clean glass dish, which may be 

 placed on a black surface. A form of porcelain dish is furnished 

 by dealers, the bottom of which is black, and which is convenient 

 for these manipulations. The smears may be made moderately 

 thick as a larger amount of sputum may thus be examined in 

 a short time. Uniform thickness is difficult to obtain and is not 

 absolutely essential. It is hardly necessary to observe that the 

 operator must be scrupulously careful not to contaminate the ma- 

 terial under examination with any kind of extraneous matter. 

 The cover-glasses and slides which are used should be new, and 

 should have been cleaned with bichromate of potassium and 

 sulphuric acid (see page 36). When the work is completed, the 

 bottle containing the sputum should be sterilized by steam or 

 boiling. 



Method for staining the tubercle bacillus: 



(a) The cover-glass or slide preparation is made, dried, and 

 fixed by passing through the flame three times. 



(b) The cover-glass, held in forceps or in a watch-crystal is 

 covered with steaming carbol-fuchsin for five minutes. If a 

 slide is employed it may be conveniently stained in the Krauss 

 staining dish, being turned face downward. 



(c) Wash in water. 



(d) Wash in alcohol containing 3 per cent of hydrochloric 

 acid one minute, or longer if necessary to remove the red color. 



(e) Wash in water. 



(f) Stain with methylene-blue solution (see page 40) thirty 

 seconds. 



(g) Wash in water. 



(h) Examine in water directly, and after drying and mounting 

 in Canada balsam. If the preparation has been made on a slide 

 it may be dried and examined directly in cedar oil with the iV in. 

 objective. When the preparation is mounted in water, tubercle 



