168 COLLODION AND OTHER IMBEDDING METHODS. 



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 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. 



304. 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 followed by chloroform. 



