VON KOCH'S COPAL METHOD. 167 



wanted for use. A stove, or the sun, may be employed for 

 drying, but it is best to dry slowly at the normal temperature. 

 The block may be preserved in good condition almost indefi- 

 nitely, the gum, when mixed with a sufficient quantity of 

 glycerin, never becoming hard or brittle. It is generally 

 better to wait till the blocks have assumed such a consistency 

 that they cannot be easily bent. It is after having waited 

 almost a week that the author always obtained the best sec- 

 tions. The gum is dissolved out from the sections by means 

 of a drop of water on the slide. The sections are then covered, 

 and a drop of glycerin being added, the preparation is com- 

 plete as soon as the water has evaporated. 



An infiltration mass. It has the advantage of being trans- 

 parent. Joliet employs it for Pyrosoma. A similar mass was 

 employed by Hertwig for Ctenophora (Jen. Zeitsch., xiv (1880), 

 pp. 313, 314 ; Journ. Boy. Hie. Soc. (N.S.), ii, p. 278). 



It would probably be advantageous to add some preserva- 

 tive substance to this mass. 



This mass can be cut dry. 



301. Strieker's Gum Method (Hdb. d. Gewebel., p. xxiv). A concen- 

 trated solution of gum arabic. The object may be prepared in alcohol and 

 imbedded in the gum in a paper case. The whole is thrown into alcohol, 

 and after two or three days may be cut. 



I have seen masses of admirable consistency prepared by this simple method. 



302. Hyatt's Shellac Method (Am. M. Micr. Journ., i, 1880, p. 8 ; 

 Journ. Roy. Mic. Soc., iii, 1880, p. 320). Prepare the object by soaking 

 in alcohol, and then put it for a day or two into a clear alcoholic solution of 

 shellac. Take a cylinder of soft wood, split it, and make a groove in one or 

 both of the half cylinders sufficiently large to admit the object without 

 pressure. Imbed in the groove with plenty of thick shellac solution, and 

 tie together the two halves of the cylinder with thread. In a day or two 

 the shellac will be quite hard ; the cylinder is then fixed in a microtome, is 

 soaked with warm water, and sections made. Should the shellac prove so 

 opaque as to interfere with a proper examination of the sections, a drop of 

 borax solution will immediately remove this difficulty. 



This process is intended for the purpose of making sections through hard 

 chitinous organs consisting of several pieces, such as stings and ovipositors, 

 retaining all the parts in their natural positions. 



303. Von Koch's Copal Method (Zool. Anz. 2, vol. i, 1878, 

 p. 36). Small pieces of the object are stained in the mass 

 and dehydrated with alcohol. A thin solution of copal in 

 chloroform is prepared by triturating small fragments of 



