CHAPTER XII. 



Methods of staining Solutions employed Preparation and stain- 

 ing of cover-slips Preparation of tissues for section-cutting Stain- 

 ing of tissues Special staining methods. 



THE entire list of solutions and methods which have 

 been recommended for the staining of bacteria are not 

 essential to the work of the beginner, so that only those 

 methods which are of most common application will 

 be given in this book. In general, it suffices to say, 

 bacteria stain best with watery solutions of the basic 

 aniline dyes, and of these, fuchsin, gentian-violet, and 

 methylene-blue are those most frequently employed. 



In practical work bacteria require to be stained in 

 two conditions : either dried upon cover-slips and then 

 stained, or stained in sections of tissues in which they 

 have been deposited during the course of disease. In 

 both processes the essential point to be borne in mind is 

 that the bacteria, because of their microscopic dimen- 

 sions, require to be more conspicuously stained than 

 the surrounding materials upon the cover-slips or in 

 the sections, otherwise their differentiation is a matter 

 of the greatest difficulty, if not of impossibility. For 

 this reason, especially in the case of section staining, it 

 frequently becomes necessary to decolorize the tissues 

 after removing them from the staining solutions in 

 order to render the bacteria more prominent ; and for 

 this purpose special methods, which provide for decolor- 

 izatiou of the tissues without robbing the bacteria of 



