108 COLLODION AND OTHER IMBEDDING METHODS. 



left to dry for from one to four days. When it has assumed a cartila- 

 ginous consistency, a block containing the object is cut out, turned over, 

 and allowed to dry again until wanted for use. A stove, or the sun, 

 may be employed for drying, but it is best to dry slowly at the normal 

 temperature. 



174. STRICKER'S Gum Method (Hdb. d. Gewebel., p. xxiv). A concen- 

 trated solution of gum arabic. The object is imbedded in the gum 

 in a paper case. The whole is thrown into alcohol, and after two or 

 three days may be cut. The alcohol should be of about 80 per cent. 

 (MAYER). 



I have seen masses of sufficiently good consistency prepared by this 

 simple method. 



175. HYATT'S Shellac Method, see Am. M. Mic. Journ., i, 1880, p. 8 ; 

 Journ. Eoy. Mic. Soo., iii, 1880, p. 320. For sections through hard 

 chitinous organs consisting of several pieces, such as stings and oviposi- 

 tors, retaining all the parts in their natural positions. 



176. BRUNOTTI'S Cold Gelatin Mass has been given, 155. 



Masses for Grinding Sections.* 



177. G. VON KOCH'S Copal Method (Zool. Am., i, 1878, p. 36). 

 Small pieces of the object are stained in bulk and dehydrated with 

 alcohol. A thin solution of copal in chloroform is prepared by 

 triturating small fragments of copal in a mortar with fine sand, 

 pouring on chloroform to the powder thus obtained and filtering. 

 The objects are brought into a capsule filled with the copal solution. 

 The solution is now slowly evaporated by gently heating the capsule 

 on a tile by means of a common night-light placed beneath it. As 

 soon as the solution is so far concentrated as to draw out into 

 threads that are brittle after cooling, the objects are removed from 

 the capsule and placed to dry for a few days on the tile in order that 

 they may more quickly become hard. When they have attained 

 such a degree of hardness that they cannot be indented by a finger- 

 nail, sections are cut from them by means of a fine saw. The sections 

 are rubbed down even and smooth on one side with a hone, and 

 cemented, with this side downwards, to a slide, by means either of 

 Canada balsam or copal solution. The slide is put away for a few 

 days more on the warmed tile. As soon as the cement is perfectly 

 hard the sections are rubbed down on a grindstone, and then on a 

 hone, to the requisite thinness and polish, washed with water, and 

 mounted in balsam. 



The process may be varied by imbedding the objects unstained, 



* For the manipulations of section-grinding, see CARPENTER'S The 

 Microscope. 



