SHERWOOD: ON DIFFERENTIAL STAINING METHODS. 29 



which may at times be found in butter. They think it would be 

 mistaken ifor the tubercle bacillus from its morphology and stain- 

 ing reactions. It could be differentiated on cultural grounds, 

 inasmuch as it grows readily on artificial media, whereas the tu- 

 bercle bacillus does not. 



Abbot and Gildersleeve'"' (1902) concluded from their study of 

 the acid-fast group that 30 per cent niti'ic acid in water is a fairly 

 satisfactory method of differentiation. They state that the ma- 

 jority of acid-fast bacteria are unable to resist decolorization with 

 this nitric acid solution, whereas it does not affect the stain in the 

 tubercle bacillus. They would also place the acid-fast organisms 

 in the group of Actinom/ycetes. In regard to animal inoculation, 

 they state that some of the acid-fast bacteria other than the 

 tubercle bacillu^ are capable of causing in rabbits and guinea pigs 

 nodular lesions suggestive of tubercles; that these lesions, while 

 often very much like tubercles in their histological structure, may 

 nevertheless be distinguished from them by the following pecu- 

 liarities : 



A. When occurring as the result of intravenous inoculation, 

 they are always seen in the kidneys, only occasionally in the 

 lungs, and practically not at all in the other organs. 



B. They constitute a localized lesion, having no tendency to 

 dissemination, metastasis, or progressive destruction of tissue, 

 by caseation. 



C. They tend to terminate in suppuration or organization 

 rather than in progressive caseation as in the case with tubercles. 



D. They are more commonly and conspicuously marked by 

 the Actinomycetes type of development of the organisms than is 

 the case with true tubercles, and these Actinomycetes are less re- 

 sistant to decolorization by strong acid solutions than are those 

 seen in tubercles. 



For the experimental work of this paper, cultures of the various 

 members of the acid-fast group were obtained from year to year, 

 from the American Museum of Natural History. A culture of 

 the tubercle bacillus was obtained from the University of Michigan 

 and one from the University of Chicago. Two cultures (two 

 strains) of the leprosy bacillus were obtained from Tulane Uni- 

 versity. Sputums from clinical cases of tuberculosis were also 

 examined. In addition to the pure cultures of B. smegmatis ob- 

 tained from the American Museum, normal smegma was secured 

 from a number of individuals and used in these experiments. 



