JOHN W. CHURCHMAN 31 



STAINING OF ACID FAST BACTERIA 



The phenomenon of acid fastness was first observed in 1881 by Neisser' in his ap- 

 plication of Weigert's staining methods to Hansen's leprosy bacillus. Bienstock and 

 Gottstein in 1886^ had called attention to the relation between this phenomenon and 

 a high lipin oontent, but it was Hammerschlag^ in 1888 who first discovered the high 

 fatty and lipin content. Aronson in 1898 showed that a large part of the ether and al- 

 cohol extractable substance was not true fat but a waxy substance. Although acid 

 fastness is not confined to the so-called "acid-fast bacteria" — since spores, the eggs of 

 certain tenia, etc., also possess the property — the phenomenon is of interest in bac- 

 teriology, chiefly as a characteristic of B. tuberculosis, B. leprae, B. smegmatis, and the 

 related avirulent species. Of the latter, about forty or fifty strains have been isolated, 

 many of them doubtless identical; there is evidence that the acid fastness of these is 

 associated with a certain common antigenic character, and all are rich in lipins. B. 

 tuberculosis differs from the saprophytes in the possession of a higher content of waxy 

 lipins. An analysis of B. leprae (Gurd and Denis)'' showed the following percentage 

 composition: 



Per Cent 



Fat, fatty acids, and cholesterol 34. 7 



Lecithin 1.7 



An explanation of the mechanism of acid fastness presents difficulties similar to 

 those encountered in attempting to account for gram staining behavior. The peculiar 

 chemical constitution of acid fast organisms suggested that their distinguishing stain- 

 ing characteristics were due to their fat content. This idea obtained generally and 

 for a long while, although there was disagreement as to whether waxes, alcohols (par- 

 ticularly the "mykol" of Tamura)^, fatty acids, or lipoid proteins were the factors ac- 

 tually concerned. As in the case of the gram stain, however, the mechanism appears 

 to be by no means a simple one, and both chemical and physical factors are doubtless 

 involved. Tubercle bacilli are impermeable to the very fat soluble dyes which readily 

 stain their isolated fats (Sudan III, scarlet R, janus green, etc.).^ On the other hand, 

 basic fuchsin (which is only slightly fat soluble), eosin and methylene blue (which are 

 not fat soluble at all), stain the individual organisms deeply in a relatively short time. 

 Corper^ showed that tubercle bacilli within tubercles do not become stained when fat 

 soluble dyes are injected into the tuberculous animals, and Sherman^ has called at- 

 tention to the well-known but often overlooked fact that an apparent staining by fat 

 soluble dyes may really be due to the staining of extra-bacillary substances and not to 

 penetration of the organisms. Such facts as these make the role of the fatty sub- 



' Neisser, M.: Virchow's Archiv., 54, 514. 1881. 



* Bienstock, B., and Gottstein, A.: Forlsch. d. Med., Nos. 6 and S. 1886. 

 3 Hammerschlag, A.: Cenlralhl. f. klin. Med. No. i. 1891. 



* Gurd, F. B., and Denis, W.: /. Exper. Med., 14, 606. 1911. 

 sTamura, S.: Ztschr.f. phys. Chemie, 89, 289. 1914. 

 ^Sherman, H.: /. Infect. Dis., 12, 249. 1913. 



7 Corper, H. J.: ibid., 11, 373. 1912. ' 



