DEMONSTRATION OF THE BACILLUS. 197 



A negation should always be withheld until every possible 

 means of finding the germ has been exhausted. A y 1 ^ inch 

 oil-immersion lens should be used, together with a mechanical 

 stage, to insure examination of all parts of the specimen. 



The sputum is collected in a clean, wide-mouthed, glass- 

 stoppered bottle. If expectoration is very scanty, the sputum 

 should be collected for the entire twenty-four hours, other- 

 wise the sputum expectorated immediately on rising in the 

 morning is taken. The sputum should be examined as soon 

 as possible. One of the small yellow nodules usually con- 

 tained in tubercular sputum is placed on a clean slide or 

 cover-glass with the platinum needle or with forceps. While 

 selecting these nodules, the sputum is placed on a black back- 

 ground to facilitate selection. The addition of a small 

 amount of carbolic acid to the sputum will coagulate the 

 albuminous masses, and one of these can be selected for 

 examination. In the absence of nodules, several loopfuls of 

 the sputum are placed on the slide. The sputum is spread 

 uniformly and as thinly as possible, dried in the air, fixed in 

 the flame, and stained in accordance with any of the methods 

 detailed in the chapter on staining. In order to obtain the 

 bacillus free from associated bacteria, the sputum should be 

 washed in sterile water as already described. 



Feces : A flake of rectal mucus or pus is examined in the 

 same manner as the sputum. It is exceedingly difficult to 

 find the tubercle bacillus in feces, and frequent examinations 

 are necessary. 



Urine : The urine is first centrifuged or allowed to settle, 

 and the sediment is then examined for tubercle bacilli. When 

 present they usually appear in bunches or masses. The 

 microscopic examination of urine or any other fluid rarely 

 gives positive results even after repeated and careful centrifu- 

 gation. It is much more satisfactory and time-saving to 

 inject the suspected material into a guinea-pig and arrive at a 

 diagnosis in that way. 



The bacillus can also be stained in sections of tissue. The 

 sections are prepared in the manner described in text-books 

 on histology, and are stained by the cold method. Decolorize, 

 counterstain, wash, dehydrate, and mount in Canada balsam. 



