48 BACTERIOLOGY 



well. It is not reliable, however, when applied to milk, as the 

 oil present in milk interferes with its operation, and milk and 

 its products quite often contains other acid-proof bacilli. The 

 smegma of the external genitals also frequently contains acid- 

 proof bacilli that are not tubercle bacilli. On this account all 

 fluids and discharges from the genito-urinary tract need to be 

 examined with particular care not to confuse tubercle baciUi 

 with smegma bacilli. Too much reliance should not be placed 

 on the possibility of distinguishing between tubercle and smegma 

 bacilli by decolorizing in alcohol. In doubtful cases an animal 

 should be inoculated. 



Patients should be given minute instructions concerning the 

 collection of sputum. The bottle used- should be new, wide- 

 mouthed, clean, and kept tightly stoppered with a clean cork. 

 The patient should be cautioned against allowing the expectora- 

 tion to get on the outside of the bottle. Probably whatever 

 risk is incurred by those who examine sputum comes chiefly 

 from the outside of the bottle having been soiled with sputum 

 containing tubercle bacilli. It is well to disinfect the exterior 

 of the bottle when it is received at the laboratory. Oftenjittle 

 white particles may be seen floating in the mucous portions of 

 the sputum. These particles should be selected for the investiga- 

 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 diflacult 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 



