44 MANUAL OF BACTERIOLOGY. 



proof or acid-fast. The most important are tubercle and 

 leprosy bacilli. There are various other species however 

 most of which are less resistant to acids and alcohol than 

 tubercle bacilli. They are discussed in the article on the 

 bacillus tuberculosis in Part IV. 



Occasionally spores of other bacteria, micrococci and 

 horny epithelial cells are imperfectly decolorized, but their 

 forms distinguish them from tubercle bacilli. Minute 

 crystalline needles which have a shape like that of bacilli, 

 are often encountered in sputum, but their nature will be 

 recognized after a little practice. 



The stain for tubercle bacilli is most frequently used for 

 specimens of sputum from cases of suspected pulmonary 

 tuberculosis ; it may be applied to other fluids and secretions 

 equally 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 contain other acid- 

 proof bacilli. The smegma of the external genitals also fre- 

 quently 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 bacilli with smegma bacilli. 

 (See smegma bacilli in Chapter IV., Part II.) 



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 allow- 

 ing the expectoration 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. Often 

 little white particles may be seen floating in the mucous por- 

 tions of the sputum. These particles should be selected for 

 the investigation, and may be spread in a thin film on the 



