HOW TO USE THE MICROSCOPE 33 



together with the sections at the bottom of the cup, to a wide- 

 mouth bottle, and covered with alcohol, glycerine, and water 

 mixture; or if it is desired to stain the specimens, they should 

 be placed in a weak alcoholic solution. 



Specimens having a hard, woody texture should be cut on 

 a sliding microtome by means of a special wood knife, which 

 is especially tempered to cut woody substances. Woody roots, 

 wood, or thick bark may be cut readily on this microtome when 

 they have been embedded by the quick paraffin process. The 

 knife in the sliding microtome is placed in a horizontal position, 

 slanting so that the knife-edge is drawn gradually across the 

 specimen. After cutting, the sections are treated as described 

 above. 



The thickness of the sections is regulated by mechanical 

 means. After a section has been cut, the block containing the 

 specimen is raised by turning a thumb-screw. In this microtome 

 the knife, as in the rotary type, is fixed, and the block contain- 

 ing the specimen is movable. 



If the specimen has been infiltrated with, and embedded in, 

 paraffin or collodion, the treatment of the sections after cutting 

 should be different. 



In the case of paraffin, the sections are fastened directly to 

 the slide, and the paraffin is dissolved by either chloroform or 

 xylol. The specimen is then placed in 100, 95, and 45 per cent 

 alcohol, and then washed in water. These sections are now 

 stained with water-stains, brought back through alcohol, cleared, 

 and mounted in Canada balsam. 



If alcoholic stains are used, it will not be necessary to de- 

 hydrate before staining, and the dehydration after staining will 

 also be eliminated. ' 



Sections infiltrated with collodion are either stained directly 

 without removing the collodion or after removal. 



FORMS OF MICROTOMES 



The hand cylinder microtome (Fig. 34) consists of a cylindrical 

 body. The clamp for holding the specimen is near the top 

 below the cutting surface. At the lower end is attached a microm- 

 eter screw with a divided milled head. When moved forward 

 one division, the specimen is raised o.oi mm. This micrometer 



