16 APPARATUS AND METHODS. 



dry in the interval between cutting and mounting it ; 

 transfer it from the razor to a watch-glass of dilute 

 alcohol, and have the drop of water or other mounting 

 fluid ready on the slide before transferring the section to 

 it. Always examine the specimen in water first, before 

 applying special reagents. If air bubbles are entangled 

 in the tissues in a section, moisten the section with weak 

 alcohol, or leave it for some time in a watch-glass of 

 weak alcohol this will at any rate remove some of the 

 air. 



13. Application of Reagents. It is always advisable 

 to have several specimens, whether whole objects or sec- 

 tions ; in the case of sections this is especially necessary, 

 so that the thinnest may be used for examination with the 

 high power. The various reagents iodine, aniline sul- 

 phate, chlor- zinc-iodine, etc. may be placed directly on 

 a slide, the specimen being then placed in the drop of re- 

 agent, and a cover lowered on the preparation, in exactly 

 the same manner as in mounting the specimen in water or 

 dilute glycerine. 



If the specimen has been mounted in water and ex- 

 amined and sketched, any one of the special reagents may 

 be applied by simply raising the cover-glass with a needle, 

 placing on the specimen a drop of the reagent, and lower- 

 ing the cover again, after washing away the superfluous 

 fluid by means of water and wiping the slide dry a little 

 outside of the specimen all round. It is often desirable, 

 however, to watch the action of the reagent without re- 

 moving the cover-glass from the specimen, and this can be 

 done by irrigation. 



14. Irrigation. To irrigate a specimen with any re- 

 agent, place a drop, or several successive drops, of the 

 reagent on the slide close to one edge of the cover taking 

 care that it does not get on to the upper side of the cover 

 and place a small torn bit of blotting-paper at the oppo- 

 site edge of the cover so as to draw the reagent through, 

 watching meanwhile for any effect produced by the reagent 

 on the specimen. Since in irrigation the reagent may fail 



