MICROSCOPIC TECHNIQUE AND REAGENTS. 763 



only or they may be prepared so as to serve for future study, 

 the latter being known as permanent mounts. 



In taking up the study of a specimen it should first be mounted 

 in water and examined ; then the water may be replaced by a weak 

 aqueous solution of glycerin (5 to 10 per cent.) and the specimen 

 examined again. After this preliminary examination other agents 

 and reagents may be employed. Specimens mounted in glycerin 

 will keep for several days and even months. Generally speaking, 

 the only efifect which the glycerin has on the tissues or contents 

 is that of swelling them, which is obviated, to a greater or less 

 extent, however, if the glycerin is washed out after an exam- 

 ination is made. 



In addition to the methods involving the use of glycerin, there 

 are two ways of making permanent mounts, depending upon the 

 employment either of Canada balsam or glycerin jelly as the 

 mounting medium. The method involving the use of the latter 

 is the simpler, and leaves the specimen in such a condition that a 

 re-examination with reagents can be made if desirable. Glycerin- 

 jelly mounts are made as follows : Specimens which have been 

 previously treated ate transferred to glycerin and allowed to 

 remain for several hours, the excess of glycerin removed, and 

 the specimen transferred to a warm slide on which a drop of 

 glycerin jelly ^ has been placed. The preparation is warmed 

 slightly to remove air-bubbles, and a warm cover-glass applied, 

 care being taken to prevent the formation of air-bubbles. Evap- 

 oration of the glycerin jelly is prevented by the use of shellac 

 cements, asphalt varnish or candlewax. 



The following method may be used for the preparation of 

 Canada balsam mounts: The specimen is cleared, dehydrated 

 by the use of alcohol and then placed in chloroform or benzol. Hie 

 clearing of the specimen is materially assisted by placing it in 

 oil of cloves or turpentine prior to mounting it. A drop of Canada 

 balsam solution (i part of balsam to 3 parts of chloroform or 



* Kaiser's Glycerin Jelly.— Digest 7 Gm. of gelatin in 42 Gm. of 

 water for two hours on a hot water-bath ; dissolve i Gm. of carbolic acid in 

 49 Gm. of glycerin; mix the two solutions; heat on a water-bath, with 

 occasional stirring, for fifteen minutes, and finally filter through glass 

 wool. The jelly is warmed slightly to hquefy it before using. 



