STAINING IN GENERAL. 153 



constant motion until the solution begins to take on a 

 brown or blackish color. Wash in water thoroughly ; 

 dry with blotting paper, and mount in balsam. 



STAINING IN GENERAL. 



The physics of staining and decolorization is hardly 

 a subject to be discussed at length in a book of this 

 character ; but, as Kiihne has- pointed out, it might be 

 said that solutions which favor the production of diffu- 

 sion currents facilitate intensity of staining, and by a 

 similar process increase the energy of decolorizing 

 agents. For example, tissues which are transferred 

 from water into watery solutions of the coloring mat- 

 ters are less intensely stained and more easily decolor- 

 ized than when transferred from alcohol into watery 

 staining fluids ; for the same reason tissues stained in 

 watery solutions of the dyes do not become decolorized 

 so readily when placed in water as when placed in alcohol. 



The diffusion of staining solutions into the proto- 

 plasm of dried bacteria, as found upon cover-slip prep- 

 arations, is much greater and more rapid than when the 

 same bacteria are located in the interstices of tissues. 

 These differences are not in the bacteria themselves, but 

 in the obstruction to diffusion offered by the tissues in 

 which they are located. 



The result of absence of diffusion may easily be illus- 

 trated. Prepare a cover-slip preparation, dry it care- 

 fully, fix it, and, without allowing water to get on it 

 from any source, attempt to stain it with a solution of 

 the dyes in absolute alcohol, washing it out subsequently 

 with absolute alcohol ; the result is negative. The ab- 

 solute alcohol does not possess the property of diffusing 



