34 STAINING REACTIONS OF BACTERIA 



granules), and chromatin. The methods for staining these substances are well known 

 and a discussion of their biological significance will be found in chapter i of this vol- 

 ume. 



STAINING OF BACTERIA IN TISSUES, ETC. 



That the immediate environment of bacteria may profoundly influence their be- 

 havior toward dyes is well known. Serum, for example, may interfere to some extent 

 with the bacteriostatic action of triphenyl-methanes; the presence of alkalies enhances 

 the staining powers of basic dyes, etc. For these reasons, bacteria in tissues, in milk 

 soil, sputum, feces, pus, do not necessarily behave toward stains as they do when 

 examined in smears from cultures, and special precautions are necessary in examin- 

 ing these materials to overcome the difficulties presented by the environment. These 

 difficulties are particularly great in examining tissues for bacteria, because the elab- 

 orate processes of fixation, hardening, and clearing may profoundly alter the bacteria 

 before they are stained. Recent studies have thrown no particular light on the 

 problems involved, and the classical methods of staining are still in use. 



STAINS IN MEDIA 



That certain aniline dyes have the power of affecting bacterial viability has long 

 been known, and their antiseptic properties have been recorded since the days of 

 Koch. Recent observations make it clear that "bacteriostatic properties" better de- 

 scribes the power of many dyes to interfere with the reproductive mechanism (gen- 

 esistasis. Churchman)' without necessarily killing or even interfering with their other 

 properties. Genesistatic potency is more striking and is more definitely established 

 than bactericidal power. Probably the most important feature of the bacteriostasis 

 produced by dyes is its highly selective character. This feature was translated into a 

 selective cultural method of great practical value by Conradi and Drigalski^ when they 

 introduced a medium for the selective cultivation of B. typhosus, by Petroff in his in- 

 troduction of a gentian-violet medium for the selective cultivation of B. tuberculosis, 

 by Krumwiede in his brilliant-green medium, etc. Of a great deal of interest and some 

 theoretical importance as regards the microchemistry of bacteria is the parallelism — 

 marked but not all inclusive — which exists between the selective bacteriostasis of 

 triphenyl-methanes and the gram reaction. Premonitions of this parallelism are 

 to be found in the observations of Stilling,^ of Dreyer, Kriegler, and Walker,"! and 

 of others; but it was first established as a general relationship by the author^ in 191 2 

 and later confirmed by Simon and Wood* and others. The mechanism of this selective 

 bacteriostasis is still obscure. The curious fact that it does not entirely parallel se- 

 lective bactericidal properties has been emphasized by Churchman^ and by Burke.* 



■ Churchman, J. W.: Proc. Nat. Acad. Sci., 9, 78. 1923. 



^ Conradi, H., and von Drigalski, W.: Zlschr.f. Hyg. u. Infcktionskrankh., 39, 283. 1902. 



3 Stilling, J.: Anilinfarbstoffe als Antiseptica, ii.s.w. Strassburg, 1890. 



^ Smith, H. W.: Am. J. Hyg., 2, 607. 1922. 



5 Churchman, J. W.: J. Exper. Med., 16, 221. 1912. 



^ Simon, C. E., and Wood, M. A.: loc. cit. 



1 Churchman, J. W.: /. Expcr. Med., 37, 543. 1923. 



* Burke, V., and Skinner, C. E.: ibid., 39, 613. 1924. 



