REAGENTS. 



8ii 



mounting medium. The method involvin 

 IS the simpler, and leav,es the specimen in 

 re-examination with reagents can be 

 made if desirable. Glycerin-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 

 remove air-bubbles, and a warm cover- 

 glass applied, care being taken to prevent 

 the formation of air-bubbles. Evapora- 

 tion of the glycerin jelly is prevented by 

 the use of shellac cements, asphalt var- 

 nish or candlewax. 



The following method may be used 

 for the preparation of Canada balsam 

 MOUNTS : The specimen is cleared, dehy- 

 drated by the use of alcohol and then 

 * placed in chloroform or benzol. The 

 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 

 benzol) is placed on a slide and the speci- 

 men mounted. When nearly dry, scrape 

 off the excess of balsam, clean the slide 

 and coverglass with chloroform or 

 benzol, and ring with cement. 



g the use of the latter 

 such a condition that a 



Fig. 328. Section of micro- 

 scope showing the relation of 

 the ocular micrometer (o) and 

 the stage micrometer (s). As 

 here represented 20 divisions 

 of the ocular scale are equiva- 

 lent to 4 divisions of the stage 

 micrometer, and thus each di- 

 vision of the ocular is equiva- 

 lent to 2 microns (see p. 813). 

 d, diaphragm in eye-piece, 

 on which the ocular microm- 

 eter rests. 



^ 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. 



