378 



Introduction to Botany. 



Method of using a razor on a simple 

 microtome. See text. 



A simple microtome, which can be clamped to the laboratory table, 

 will be found of great service. '^ 



In cutting sections with such an instrument, the razor is to be held 



firmly, edge and back, against the 

 / glass top, and given a sliding forward 

 motion, as indicated by the arrow in 

 Fig. 202. The object, embedded in 

 elder pith, if necessary, is clamped in 

 the object holder, which, as the sec- 

 tions are cut, is raised by means of a 

 micrometer screw to the desired thick- 

 ness of the sections. 



246. Mounting the Sections. — As 

 a rule a section should be mounted 

 for study in a drop of water under a 

 coverglass, and, if reagents are to be 

 used, they are added afterward. The 

 drop in which the section is to be 

 mounted should be of such a size 

 that it will fill the space under the 

 coverglass and no more ; if too much has been added, draw away the 

 surplus with filter paper ; if not enough, place a small drop on the slip 

 close to the coverglass on the side where the water comes to the edge, 

 and then draw the drop into contact with the coverglass by means of 

 a dissecting needle or small stick. If the drop is placed at first in con- 

 tact with the coverglass it may run over its upper surface ; if it is placed 

 on the side where the water does not fill out to the edge, it is likely to 

 entangle air bubbles when it runs under. If no reagents are to be used, 

 the preparation may be kept from drying by applying a drop of 50 % 

 glycerine to one edge of the coverglass, so that it may take the place 

 of the evaporating water. 



247. Applying Reagents. — Any reagent miscible with water, such as 

 a solution of iodine, may be made quickly to replace the water in which 

 the section is mounted, by placing a drop of the reagent on the slip in 

 contact with the edge of the coverglass, and then placing a strip of 

 filter paper in contact with the opposite edge ; in this way the water is 

 drawn out and the reagent flows in and occupies its place. 



248. Sharpening Knives and Razors. — No satisfactory results can 



1 See catalogue of Bausch & Lomb, Rochester, N.Y. 



