228 THE MICROSCOPIST. 



preparation can be mounted in glycerin, balsam, or dam- 

 mar (Chapter YI). In fixing the cover to specimens 

 mounted in glycerin it may be useful to apply liquid glue 

 or strong gelatin solution to the edges, using the turn- 

 table or otherwise, and after it is dry to cover it with 

 some other cement. Any glycerin which may accident- 

 ally be on the cover had better be left until the glue has 

 dried, when it can be removed by a camel's hairbrush and 

 water. 



Dr. Beale recommends that nitrate of silver, chloride 

 of gold, osmic acid, etc., when used for staining fine tis- 

 sues, should be dissolved in glycerin. Less than J per 

 cent, solution of gold, etc , will thus bring out details 

 which are scarcely attained otherwise. The time of soak- 

 ing and strength of the solution varies according to the 

 tissue and effect desired. 



The most delicate sections are made by freezing speci- 

 mens after they have been well saturated with a strong 

 solution of gum arabic. For this purpose Professor 

 Rutherford's freezing microtome has been invented, in 

 which the cylinder of the ordinary section-cutter, page 

 63, is surrounded by a reservoir for powdered ice and salt, 

 so as to freeze the tissue. Dr. Beale recommends freez- 

 ing by the use of nitrous oxide gas, and Dr. Pritchard 

 has suggested a metallic cylinder with a wooden handle, 

 which can be cooled below the freezing-point by salt and 

 ice. A small piece of tissue will immediately freeze on 

 the metal so as to be cut into thin sections by hand. If 

 thawing sets in it may be covered with thin gutta-percha 

 and plunged into the ice and salt. 



Dr. S. Marsh, in an excellent little treatise on section- 

 cutting, recommends that the knife should not be ground 

 flat on one side, but be slightly concave on each side. In 

 cutting it is necessary to keep the blade well flooded with 

 spirit, except in using the freezing microtome. The sec- 

 tions are best transferred to a basin of water, and lifted 



