JOHN W. CHURCHMAN 27 



5. Not even all strains of a given species necessarily behave exactly alike toward 

 dyes. The existence of "strains-within-a-species variants," as measured by the bac- 

 teriostatic effect of gentian violet, has been described; and from a given pure culture 

 of B. coli two strains have been isolated — one dye sensitive and the other not — which 

 were identical in all cultural, morphological, and tinctorial respects ("strain-within-a- 

 strain variant").' 



The facts are that the properties of the two groups stated in the foregoing table 

 are probably to be regarded as "independent variables in the sense that any one of 

 them may be possessed by a particular strain of bacteria independent of the other 

 properties of that group." None the less, as Smith has stated, "this almost clear sep- 

 aration of the families of bacteria on the basis of biochemical reactions cannot be 

 without significance." 



It is inevitable that the dilemma as to the physical or chemical nature of staining 

 which we have encountered in discussing the general mechanism of the staining proc- 

 ess must also be faced in discussing the method of Gram. On the whole, the tendency 

 is to emphasize the chemical rather than the physical factors of this reaction, and 

 many observers (e.g., Deussen)^ regard the process as purely chemical. That physical 

 structure is also involved seems none the less certain. Benians^ has shown that bac- 

 terial disintegration induced by mechanical measures upsets the gram behavior; 

 Churchman has shown that certain organisms (e.g., B. anthracis) are gram positive 

 only in the cortex, which may be removed by chemical means, exposing a gram nega- 

 tive medulla ; and that some sort of bacterial membrane plays a physical part in the 

 process is taken for granted in most of the theories which attempt to account for the 

 phenomenon. Benians has been the chief exponent of a purely physical explanation of 

 the gram stain and has advanced perhaps the most convincing evidence for this view. 

 From experiments in which bacteria were studied after disintegration by crushing, 

 Benians^ drew the following conclusions: 



1. The gram positive property is inherent in the physical structure of the bacte- 

 rial cell, and — since mordants are not essential — is not conferred on it by the mordant. 



2. Nothing in the nature of chemical fixation of the compound dye to bacterial 

 substance occurs. 



3. The effect of the mordant is to dissociate dye from its adsorption compound 

 with the tissues, forming with it a large, compound molecular body which in alcoholic 

 solution does not easily pass out of the gram positive bacteria. This conception of the 

 role of the mordant supplanted Benians' earlier idea that it acted by preventing al- 

 cohol from entering the cell. 



4. Capacity for retaining the compound dye is chiefly dependent on the structure 

 and integrity of the limiting membrane. 



5. The essential character of the gram positive cell membrane is that it does not 



' Churchman, J. W., and Michael, W. H.: ibid., 16, 822. 191 2; Churchman, J. W.: ibid., 33, 

 569. 1921. 



^Deussen, E.: loc. cit. 



3 Benians, T. H. C: J. Path. & BaQi., 17, 199. 1912. 



''Benians, T. H. C: ibid., 23, 411. 1919-20. 



