436 PEACTICAL DIRECTIONS. [APP. 



c. Mounting sections. 



When the sections are cut, place them iii 

 rows on a slide prepared in the following manner. 

 Make a solution of white shellac in kreasote 

 by heating, and let it be of the consistency of 

 glycerine, or slightly more fluid. "With a camel's 

 hair-brush paint a very thin and unifoim layer 

 of this gum over the slide which must be clean 

 and dry, and while the gum is wet place the sec- 

 tions in rows upon it. Now place the slide on a 

 water bath which is heated up to the melting 

 point of the paraffin. The sections sink down 

 into the thin layer of shellac and kreasote, the 

 kreasote slowly evaporates and the shellac be- 

 coming hard fixes the section in the position in 

 which it was placed on the slide. When the 

 kreasote has been evaporated, pour turpentine 

 carefully upon the slide, this dissolves the pa- 

 raffin and clears the sections which may at once 

 be mounted in canada balsam. 



A turpentine or chloroform solution of canada balsam 

 should be used. 



This method of cutting ribbons of sections 

 was first introduced by Mr Caldwell, to whom 

 we are also indebted for the account given above 

 for mounting sections (vide Note B, p. 471). 

 The latter however is a modification and im- 

 provement of Dr Giesbrecht's method. {Zoolo- 

 gischer Anzeiger No. 92, 1881.) 



C. Preservation of the embryo as a wJiole. 



Chick embryos of the first or second day may be 

 easily preserved whole as microscopic objects. For 

 this purpose, the embryo, which has been preserved 



