26 THE UNIVERSITY SCIENCE BULLETIN. 



been taken advantage of by bacteriologists and made use of in the 

 routine laboratory examination of sputum, urine, pus, etc., for 

 tubercle bacilli in suspected cases of tuberculosis, and by many in 

 examining butter, milk and other foods for the presence of tubercle 

 bacilli. Now, as was stated above, this acid-fastness or acid- 

 proof ness is not the property of just one organism but of a small 

 group of organisms. It has been the aim of many workers to find 

 some method of decolorization that would enable one to differ- 

 entiate between true tubercle bacilli and other members of this 

 group. This seems to be desirable in order to eliminate possibili- 

 ties of error in the laboratory examination of suspected tubercu- 

 lous material, since the smegma bacillus is very commonly found 

 in normal smegma, and has been reported as found, occasionally, 

 in gangrenous conditions of the lungs, on the tonsils, in the tartar 

 from the teeth, from scrapings from the tongue, and on the skin 

 in the inguinal and axillary regions. The butter bacillus and 

 grass bacillus may be present in butter, in other dairy products, 

 and foods. Hence, either of these last two organisms may be 

 found present in the mouths of normal individuals. Since tuber- 

 culosis is caused only by the tubercle bacillus and not by any 

 other members of the acid-fast group, it is desirable when exam- 

 ining suspected material to rule out possibilities of error due to 

 the presence of these other organisms. Many staining methods 

 have been suggested, tried and recommended. They may be 

 grouped into five groups as to theories and methods: 



1. That true tubercle bacilli differ from the rest of the acid- 

 fast group in their resistance to decolorization with 25 or 30 per 

 cent aqueous solution of the mineral acids. All of the acid-fast 

 organisms, excepting true tubercle bacilli, are said to be decolor- 

 ized. 



2. That while this group is acid-fast, only true tubercle bacilli 

 are acid-alcohol fast. Hence, acidulated alcohol (2 to 3 per cent 

 hydrochloric or nitric acids in from 70 per cent to absolute alcohol) 

 has been used as a differential agent. 



3. Some modification of (2), such as Pappenheim 's, where 

 rosalic acid is used in connection with glycerine and absolute 

 alcohol. 



4. That it is necessary and important to remove the fats and 

 use strong concentrations of mineral acids and absolute alcohol 

 to decolorize everything except the tubercle bacillus. 



5. Fonte's method, which is a combination of the acid-fast 

 and Gram's stain, as described below. 



