142 BACTERIOLOGY. 



above the flame and removed from it at the first evidence 

 of vaporization, or, better still, a little before this point is 

 reached. We have derived no advantage from the 

 addition of acids or alkalies to the mordant as recom- 

 mended by Loffler, but obtain with a fair degree of 

 regularity satisfactory results through the use of the 

 neutral mordant alone.^ 



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 decjolorized 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- 



1 I am indebted to Dr. James Homer Wright, Thomas Scott Fellow in 

 Hygiene, 1892-93, University of Pennsylvania, for the suggestions in connec- 

 tion with the modification of this method. 



