8o4 BOTANY AND PHARMACOGNOSY. 



Double Staining, or the use of two stains in the examination 

 of a specimen, furnishes not only a means of beautifying the speci- 

 men, but also has a certain diagnostic value. The following are 

 some of the combinations used: (a) aqueous solutions of car- 

 mine in connection with alcoholic solutions of iodine green; (b) 

 alcoholic solutions of hsematoxylin and safranin; (c) solutions of 

 eosin and methylene blue; (d) solutions of fuchsin and methylene 

 blue; (e) solutions of gentian violet and Bismarck brown. 



MOUNTING OF SPECIMENS.— Microscopic preparations 

 or mounts are of two kinds : they may serve a temporary pur- 

 pose 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 effect 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 tlje 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. Glyc- 

 erin-jelly MOUNTS are made as follows : Specimens which have 

 been previously treated are 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 



' Kaiser's Glycerin Jelly. — Soak 7 Gm. of gelatin in 42 Gm. of water 

 for two hours ; 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 liquefy it before using. 



