REAGENTS AND PROCESSES 543 



and in this way facilitates the study of these bodies. About I Gm. of gelatine 

 is dissolved in 100 mils of water; a drop of this is placed upon a slide which has 

 been somewhat warmed, and then a drop of the fluid containing the motile bodies 

 is added to the drop of gelatine solution and mixed with it by stirring, after which 

 the cover-glass is 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 instan- 

 taneously fixing and staining the nuclei of fresh tissues. Anthers and sporangia 

 need only to be tested out with needle in this fluid or crushed under the cover-glass, 

 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 under Double Staining and 

 Gram's Method. 



Glucose. A mounting medium is made from glucose by mixing 140 parts of 

 distilled water with 10 parts of camphorated alcohol, 40 parts of glucose, and 10 

 parts of glycerine. The water, glucose, and glycerine are first mixed, and then the 

 alcohol is added and the mixture filtered to remove any camphor which may have 

 been precipitated. The aniline stains are preserved particularly well in this medium. 



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 cover-glass 

 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 cover-glass 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 cover-glass. 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 

 stains, such as the carmine stains, an acidulation with i per cent, of acetic acid is 

 of advantage. 



Dilute glycerine, in which sufficient chrome-alum has been dissolved to give a 

 clear blue color, is recommended as a mounting medium for the Schizophyceae and 

 Florideae, since the natural colors of these plants are retained in this medium. 



Sections containing mucilaginous membranes may be mounted in a drop of pure 

 glycerine in which the membranes will not swell, and then, by irrigating the mount 

 with water, the process of the slow swelling of the membrane may be observed. 



Glycerine-gelatine. This is for most subjects a better mounting medium than 

 glycerine alone. It is prepared as follows : One part by weight of the best gelatine 

 is soaked for about two hours in 6 parts by weight of distilled water. Then 7 parts 

 by weight of chemically pure glycerine are added, and finally, to each 100 Gm. of 

 this mixture i Gm. of concentrated carbolic acid. The mixture is warmed for 

 about fifteen minutes, and at the same time constantly sitrred until it becomes 

 clear ; then, by means of a hot- water funnel, or while kept warm in an incubator, the 

 mixture is filtered through glass-wool or filter paper which has been washed with 

 distilled water after being placed in the funnel. 



To mount sections in glycerine-gelatine the glass slip is warmed and a small bit 

 of the gelatine is placed upon it. If the slip is not warm enough to melt the gela- 



