138 BACTERIOLOGY. 



For other organisms one must determine whether the 

 results are better after the addition of acid or alkali, 

 and how much of either is required. In general it may 

 be said that bacteria which produce acids in the media 

 in which they are growing require the addition of alka- 

 lies to the mordant, while those that produce alkalies 

 require acids to be added. By following Loffler's direc- 

 tions the delicate, hair-like flagella? on motile organisms 

 may be rendered plainly visible. 



STAINING IN GENERAL. 



The physics of staining and decolorization is hardly 

 a subject to be discussed in a book of this character, but, 

 as Kiihne has pointed out, 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 matters are less intensely stained and more 

 easily decolorized than when transferred from alcohol 

 into watery staining fluids ; for the same reason tissues 

 staiued 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- 



