SPECIAL METHODS 141 



easy to mount a thick section between 2 lantern slides of the same size, 

 on account of the balsam which oozes out at the edges. Such prepara- 

 tions may be used directly as lantern slides. Large sections of the 

 stem of a tree fern make good mounts without any staining. 



STONY TISSUES 



Sections of the stony tissues of hickory nuts, walnuts, peach stones, 

 and similar refractory substances cannot be cut by ordinary methods. 



With a fine saw, saw sections about 1 mm. in thickness. Put some 

 fine carborundum on a piece of plate glass, wet it, lay the section on it 

 and, with the finger on the section, rub with a circular motion until one 

 side of the section is quite smooth. Turn the section over and rub the 

 other side. When the section has become quite thin (about half a 

 millimeter) use a piece of plate glass, about 10 cm. square, instead of 

 the finger. When the section is thin enough, wash it thoroughly, de- 

 hydrate, clear, and mount in balsam. 



The long, narrow pores show better without any clearing. In this 

 case, dry the section thoroughly, heat a few drops of balsam on the 

 slide to drive off the solvent, put the section into the balsam, and add 

 a cover. The air caught in the long, narrow pores will make them ap- 

 pear as black lines. Sections of most nuts show excellent detail with- 

 out any staining. Thin sections, however, may be stained in the usual 



way. 



STEAM METHOD FOR HARDWOOD SECTIONS 



In 1926 Dr. Josef Kisser published a useful method for cutting sec- 

 tions of hard woods. The method consists, essentially, in letting steam 

 play upon the block as the sections are being cut. The hot steam is 

 easily secured by a simple apparatus which can be set up in a few min- 

 utes in any laboratory. All that is needed is a flask, holding about 300 

 c.c, and some glass tubing (Fig. 25). The temperature of the steam 

 should be about 90° C. If the steam is too hot, the material dries; if 

 the temperature is much below 90° C, there is little advantage from 

 the steam. 



The Spencer Lens Company's holder for thin safety razor blades, 

 while excellent for thin paraffin sections, does not hold the thin blade 

 so well for wood sections. However, the holder holds the Durham du- 

 plex blade very well, and the Gem or Star blade, with the back broken 

 off, is ideal for wood sections. Of course, if one likes to sharpen micro- 

 tome knives, they are long and will cut while they are sharp. 



