STAINING IN GENERAL. 177 



jority of other bacteria by the tenacity with which it 

 retains the color when treated in this way ; it is an 

 organism difficult to stain, but when once stained is 

 equally difficult to rob of its color. 



STAINING IN GENEKAL. 



The physics of staining and decolorization is hardly 

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

 character; but, as Kuhne has pointed out, it may be 

 briefly said that solutions which favor the production of 

 diffusion-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 in the protoplasm 

 of dried bacteria, as found upon cover-slip preparations, 

 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 illustrated : 



Prepare a cover-slip preparation, dry it carefully, 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 subsequently with 



12 



