206 COLLODION AND OTHER IMBEDDING METHODS. 



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 aside 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 un- 

 stained, 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. In this way von Koch was able to demon- 

 strate the most delicate lamellae of connective tissue in Isis 

 elongata. 



This method was imagined in order to enable the hard and 

 soft parts of corals to be studied in their natural relations. 

 It is evidently applicable to the study of any structures in 

 which hard and soft parts are intimately combined. It is 

 certainly a method of the very greatest value. 



312. Ehrenbaum's Colophonium and Wax Method (Zeit.f. wiss. 

 Mik.j 1884, p. 414). Ehrenbaum recommends that the objects 

 be penetrated by a mass consisting of ten parts of colophonium 

 to one 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 fol- 

 lowed by chloroform. 



313. Weil's Canada Balsam Method (Zeit. f. wiss. Mik., v, 2, 1888, 

 p. 200). Balsam heated till brittle when cold, then dissolved in chloroform. 

 Heat the objects in the mass on a water-bath. For further details see 

 Journ. Roy. Mic. Soc., 1888, p. 1042. 



