CHAPTER V 

 STAINING 



THIN sections of light-colored specimens, especi- 

 ally those prepared by the infiltration method, are 

 apt to be so transparent that the details of structure 

 are almost invisible. This difficulty is overcome by 

 coloring or staining the sections with various dye- 

 stuffs. The staining process is either a saturation 

 of the cellular material with the color, or a chemical 

 reaction between the stain and the compounds con- 

 tained in the cell. In the latter instance the stain plays 

 the part of a reagent. As a rule the nuclear material 

 stains more readily than the other parts of the cell; 

 therefore upon the application of a saturation or general 

 stain, the nucleus will always appear more deeply 

 colored than the surrounding parts. 



With comparatively few exceptions the stains in 

 use are aniline colors and are kept in the form of satu- 

 rated alcoholic solutions. These solutions should be 

 kept in glass-stoppered bottles hi a dark cool place. 

 The staining solutions are prepared by diluting 5 mils 

 of the alcoholic solution with distilled water, to make 

 100 mils. If sections are hi aqueous media and not 

 attached to slides, they may be stained by placing them 

 in a shallow dish filled with the stain. If the sections 

 are dehydrated, whether attached to slides or free, they 

 must be rehydrated as directed in a previous chapter. 



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