ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 355 



filtered wliile hot through a suitable apparatus. It is not advisable 

 to add any antiseptic. The coUodionized plate is now immersed in 

 the vessel containing the hot gelatin, and when the collodion and 

 gelatin have united (the disappearance of all streaks from the collo- 

 dion surface shows this), the section, previously kept in distilled water, 

 is placed thereon by means of a fine brush. The plate is then 

 removed from the bath, and laid carefully in a horizontal position. 

 If the gelatin layer and the section both be thin, 12 to 18 hours are 

 sufficient to dry them. Should any part of the section remain un- 

 covered, a fresh layer of gelatin solution, at a temperature of 50*^, 

 may be poured over the plate, held in a sloping position. 



Drying may be considered completed when the preparation is 

 quite transparent, and the gelatin surface so firm that it no longer 

 receives the indent of the finger-nail. The gelatin layer may now 

 be marked, if need be, with ordinary ink. Finally, a second collo- 

 dion layer is run over the gelatin. Endeavour should be made to 

 keep the second layer about as thick as the first. After drying 

 again, the gelatin-collodion layers are stripped off the glass plate by 

 cutting first along the edge, and then raising the collodion-gelatin 

 layers with a scalpel. If the glass plate have been properly cleaned, 

 this is quite easily done. As the collodion-gelatin layers tend to 

 curl up, it is advisable to submit them to a certain pressure. This is 

 best done by placing them between the leaves of a pretty thick book. 



With care, 200 sections of the pons varolii may be mounted in 

 one collodion-gelatin layer. The author's researches were chiefly 

 devoted to the central nervous system. He found that preparations 

 treated with Miiller's fluid, and afterwards with perchloride of 

 mercury, gave better results than when nervous tissue had been 

 hardened in alcohol, and especially if kept for any length of time. 

 The chief advantages of this method consist in the transparency of 

 the sections and the ease with which they are preserved. Low 

 powers are quite sufficient to enable the course and distribution of 

 the nervous fibres to be followed with ease. The only inconvenience 

 complained of by the author is the impurities which commercial 

 gelatin contains. These, however, are no bar to microscopical 

 investigation. 



White Rosin as a Mounting Medium.* — Mr. H. L, Brevoort 

 reports the results of his experiments in mounting with white rosin 

 to be very satisfactory. The method is the following: — On the 

 centre of a clean glass slide, laid on the heating table, put a small 

 piece of rosin of the purest quality. Heat is gently applied until 

 the rosin becomes as liquid as it can be made without burning it. To 

 remove air-bubbles, with a pointed glass rod add to the liquefied rosin 

 and stir in with it, a half-drop of turpentine. A moment or two 

 after the object to be mounted has been placed in the medium, and 

 the cover-glass has been dropped upon it, the slide must be removed 

 from the hot table, and a spring clip applied. In five minutes the 

 mount will be ready for finishing and labelling. For such objects 



* Journ. New York Micr. Soc, i. (1885) pp. 202-3. 



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