110 CELLOIDIN 



We have seen masses of sufficiently good consistency prepared by this 

 simple method. 



200. Hyatt's Shellac Method, see Am. Mic. Journ., i, 1880, p. 8 ; 

 Journ. Roy. Mic. Soc, Hi, 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. 



201. Brunotti's Cold Gelatin Mass has been given, § 180. 



MASSES FOR GRINDING SECTIONS* 



202. G. VON Koch's Copal Method {Zool. Anz., 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 tlireads 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 bone, to the requisite thinness and 

 polish, washed with water, and mounted in balsam. 



The process may be varied by imbedding the objects unstained, 

 removing the copal from the sections by soaking in chloroform, 

 decalcifying them if necessary, and then staining. 



It is sometimes a good plan, after removing the copal, to cement 

 a section to a slide by means of hard Canada balsam, then decalcify 

 cautiously the exposed half of the specimen, wash, and stain it. 



This method was invented in order to enable the hard and soft 

 parts of corals to be studied in their natural relations, and is 

 valuable for this and similar purposes. 



203. Ehrenbaum's Colophonium and Wax Method {Zeit. iviss. Mik., 

 1884, p. 414). Ehrenbauni recommends a mass consisting of 10 parts 

 of colophonium to 1 of wax. The addition of wax makes the mass less 

 brittle. Sections are obtained by grinding in the usual way. The mass 

 is removed from them by means of turpentine followed by chloroform. 



* For the manipulations of section-grinding, see Carpknter's The 

 Microscope, and §§ 910 et seq. 



