304 REAGENTS AND PROCESSES 



in TOO c.c. of water; a drop of this is placed upon a slide which 

 has been somewhat warmed, and then a drop of the fluid con- 

 taining the motile bodies is added to the drop of gelatine solu- 

 tion and mixed with it by stirring, after which the coverglassis 

 put on. See also under Nutrient Media. 



Gentian Violet. A i or 2 per cent, solution of acetic acid, 

 to which gentian violet is added until the solution appears of 

 a deep violet color, is effective in instantaneously fixing and 

 staining the nuclei of fresh tissues. Anthers and sporangia 

 need only to be teased out with a needle in this fluid or 

 crushed under the coverglass, when the nuclei of the pollen 

 grains and spores or the mother cells of these will be fixed 

 and stained for immediate examination. See also page 264 and 

 Gram's Method. 



Glycerine. This is frequently used as a mounting medium, 

 but since objects are apt to become very transparent in it, only 

 those sections which have been stained should be mounted in 

 it. Sections, such as of wood, which are not apt to shrink easily 

 may be mounted in glycerine directly from water, but delicate 

 tissues should first go from water into a mixture of 10 parts of 

 water and i part of glycerine; this should then be allowed to 

 concentrate by the evaporation of the water, when the sections 

 may be mounted on the slide in a drop of pure glycerine. The 

 coverglass should be quite clean and the glycerine should not 

 be allowed to run back over it. After putting on the cover- 

 glass the surplus glycerine should be taken up with a bit of filter 

 paper and the slide about the edge of the coverglass should be 

 made quite clean with a cloth moistened in water and then wiped 

 dry with a dry cloth; then the slide may be put in position on the 

 turntable, where a ring of Brunswick black, or of shellac to each 

 ounce of which 20 drops of castor oil have been added, may be 

 spun around the edge of the coverglass. This process should 

 be repeated several times, allowing each coat to harden before 

 putting on the next, until a strong ring of the cement has been 

 formed. When certain stains are used, such as haematoxylin, 

 the glycerine must be entirely free from acids; but with other 



