SECTION STAINING 127 



carbol-thionine blue, the staining taking from a few 

 minutes to half an hour. If a contrast stain be desired, 

 the sections may be treated for a few seconds with the 

 eosin solution after the dilute acetic. If staining be pro- 

 longed, evaporation must be prevented by covering the 

 watch-glass of stain, or by placing the slide flooded with 

 stain on a piece of wet blotting-paper on a tile and covering 

 with the lid of a Petri dish. 



The micro-organisms in sections stained with these 

 blues are very liable to become decolorised unless the 

 dehydration is expeditiously performed. To avoid this 

 Unna's method may be adopted. After staining and 

 decolorising with acidulated water as described, the 

 sections are placed on the slide (if not already mounted 

 thereon), gently warmed, and so dried ; they are then 

 treated with xylol and mounted in balsam. The tissue 

 elements, however, are apt to suffer. 



A better method is to dehydrate with anilin instead of 

 with alcohol, the section being treated with fresh anilin 

 two or three times, then with a mixture of equal parts of 

 anilin and xylol, and finally with xylol. 



Capsule Staining 



Many organisms, especially in the tissues or body fluids, 

 are invested with a capsule of gelatinous matter, probably 

 derived from the membrane of the bacterial cell, and 

 differing in composition in different species. The capsule 

 may be as thick as the bacterial cell itself, and appears, 

 in the unstained state or after staining by the ordinary 

 methods, as a clear halo or zone surrounding the organ- 

 ism. Organisms in films of albuminous matter often 

 appear to be surrounded by a clear halo, which must not 

 be mistaken for a capsule. As organisms frequently lose 

 their capsules on ordinary culture media, Moor recom- 



