GLYCERINE-GELATINE 305 



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 mount- 

 ing medium for the Schizophycese 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 2 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 15 minutes, 

 and at the same time constantly stirred 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 gelatine, it should be passed back 

 and forth above the flame of an alcohol lamp. If the sections are 

 of a character not liable to shrink, they may be transferred 

 directly from water to the melted gelatine; if, however, there 

 is danger of shrinking, the sections should first be placed in a 

 10 per cent, solution of glycerine, which is then allowed to con- 

 centrate by evaporation of the water, and then, from the concen- 

 trated glycerine the sections may be transferred to the drop of 

 melted glycerine-gelatine. To avoid air-bubbles the cover- 

 glass should be put on with the precautions given on page 265 

 for putting on the coverglass when Canada balsam is the mount- 

 ing medium. If several sections are being mounted under 



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