CHAPTER IX. 109 



removing the c< pal 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. 



178. EHRENBAUM'S Colophonium and Wax Method (Zeit. wiss. 

 Mik., 1884, p. 414). Ehrenbaum 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. 



179. JOHNSTONE-LAVIS and VOSMAER'S Balsam Method (Journ. 

 Roy. Mic. Soc., 1887, p. 200). Alcohol material is carefully and 

 gradually saturated, first with benzol, and then with thin and thick 

 solution of benzol-balsam. It is then dried for a day in the air and 

 for several days more in a hot-air bath. When hard it is ground in 

 the usual way. 



180. WEIL'S Canada Balsam Method, see Zeit. wiss. Mik., v, 1888, 

 p. 200. 



181. GIESBRECHT'S Shellac Method. For hard parts only, spines 

 of Echinus, shell, etc., see Morph. Jahrb., vi, 1880, p. 95, or the abstract 

 in LEE und MAYER, Grundzuge. 



Congelation Masses. 



182. The Methods of Freezing. For the requisite manipulations 

 and means of producing the requisite degree of cold, see CARPENTER'S 

 The Microscope (ether spray) ; JOHNE, Zeit. wiss. Mik., xiv, 1897, 

 p. 370 (liquid carbonic acid) ; WOLFF, ibid., xxv, 190S ; p. 175 (ethyl 

 chloride) ; KRAUSE, ibid., p. 289 (solid carbonic acid) ; JUNG, Verb. 

 Ges. Naturf. Aertze, Ixix, 1898, p. 129 (ethyl chloride) ; BRISSY, 

 C. R. Soc. BioL, Ixii, 1907, p. 1115 (liquid air). 



Fresh tissues may be, and are, frequently frozen without being 

 included in any mass. But the formation of ice crystals frequently 

 causes tearing of delicate elements, and it is better to infiltrate the 

 tissues with a mass that does not crystallise in the freezing mixture, 

 but becomes simply hard and tough, such as one of those given below. 



When sections have been obtained, it is difficult to manipulate 

 them. OLT (Zeit. wiss. Mik., xxiii, 1906, p. 327) puts them into a 

 1 per cent, solution of gelatin, brings them therein on to a slide, 



