NEW METHOD FOR GRAM STAIN 171 



organisms are thoroughly decolorized, with the possibility of 

 reducing the brilliancy of the dye in the Gram positive organisms 

 and relying upon a weak counter stain not to mask the dye in 

 the (jram jiositive organisms. The degree of contrast is the 

 same in both cases but I prefer the former method with a strong 

 counter stain like Safranm O which brings out the Gram negative 

 organisms very distinctly and stains them a color which contrasts 

 more shai-ply with the blackish purple of the Gram positive organ- 

 isms than that of some other counter stains. I find it easier to 

 make a decision and study the morphology if both tjTies of 

 organisms are heavily stained with distinct colors than if both 

 are more weakly stained with distinct colors or if one tjrpe is 

 intensly and the other very faintly stained. 



XYLOL 



Clearing the stained film in xylol or turpentine improves the 

 definition, thereby making it easier to separate the Gram positive 

 from the Gram negative organisms and to study the morphology. 

 It is of particular value in the examination of pus and mixed cul- 

 tures. By clearing the organism in this manner instead of 

 depending upon the immersion oil one can more readily determine 

 whether the density of color in some of the questionable organ- 

 isms is due to a mixture of the violet dye with the counter stain, 

 or to a masking of the violet dye by the counter stain, or to an 

 excessive concentration of the counter stain. 



GRAM REACTION 



The phenomenon of the Gram reaction has been explained 

 upon both a chemical and a physical basis. The chemical 

 explanation of the reaction is that the dye, iodine and protein 

 of the cell of the Gram positive organisms form a comparatively 

 insoluble compound. The physical explanation is based upon 

 the assumption, supported by some convincing experiments, 

 that the phenomenon depends upon the nature of the cell mem- 

 brane and the size of the molecules in the dye iodine precipitate, 

 the molecules in solution in the decolorizer being unable to 



