ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 169 



in the slightest degree the back from the stone ; and further the knife 

 must not be pressed on the stone, but held lightly by the finger-tips, 

 and the necessary friction be left to capillary adhesion. After draw- 

 ing the knife fifteen to twenty times it should be tested as before. 



The knives furnished with the Thoma microtome should be pro- 

 vided with a wire support (fig. 44 to) for the back of the knife during 

 the process of sharpening. 



Chrome Mucilag-e as a Fixative.* — Dr. J. Frenzel recommends 

 the following process : — Make a thin solution of gum arabic in water 

 and add to this an aqueous solution of chrome alum. An excess of 

 the latter does no harm. A little glycerin is added to the mixture to 

 prevent it from drying too rapidly when painted on the slide. 



After painting the slide with a small brush the sections are 

 placed in order and the slide left for a few minutes (not over 

 fifteen minutes) in the oven of a water-bath kept at 30-45^ C. 

 The gum is thus rendered insoluble. The paraffin is next renjoved 

 in the ordinary way, and the sections stained according to desire. 

 Fuchsin and safranin are the only anilin dyes which cannot be used, 

 as they stain the film of gum deeply, and thus injure the preparation. 



Fixing Serial Sections on the Slide.f — For this purpose gutta- 

 percha dissolved in benzol and chloroform ; caoutchouc dissolved in 

 benzol ; gum arabic ; gum arabic dissolved in absolute alcohol ; and 

 collodion one part with three parts oil of cloves ; have been used. 



Dr. H. Leboucq's modification consists in combining the last two 

 methods. He covers a warmed slide first with gum, and then with 

 collodion. Sections still retaining their paraffin are placed upon the 

 slide and the latter upon a glass plate warmed by a lamp. As soon 

 as the paraffin is melted it is removed by means of turpentine oil or 

 benzol, and finally the sections are mounted in Canada balsam. 



Treatment of Sections with Osmic Acid. | — Herr F. Stuhlmann 

 has devised a method of treating tissues with osmic acid after they 

 have been cut (by the paraffin method) and placed on a slide smeared 

 with Mayer's solution of albumen and glycerin. 



A few drops of the acid are placed in a watch-glass and the slide 

 laid across it with the sections downwards ; the whole is covered with 

 a bell-glass to avoid undue evaporation, and kept for half an hour to 

 an hour and a half. They are then stained a pale yellow, which 

 is sufficient, but it is sometimes useful to stain them further with a 

 watery solution of hsematoxylin. The method is particularly useful 

 for nerve-tissues. 



Staining Nerve-fibres of Retina.§ — Dr. S. Bernheimer colours 

 pale nerve-fibres, especially those of the retina, with hasmatoxylin in 

 the following manner. 



* Amer. Natural., xis. (1SS5) p. 12i6. From Arch. f. Mikr. Anat., xxv. 

 (18S5) p. 52. 



t Ann. Soe. Med. Gand, 1884, pp. 167-8. Cf. Vircbow and Hirsch'a 

 Jahresbericht (for 1884) 1885, p. 41. 



X Zool. Anzeig., viii. (1885) pp. 643-4. 



§ SB. K. Akad. Wiss. Wien, xc. (1884) 6 pp. Cf. Virchow and Hirsch's 

 Jaliresbericht (for 1884) 1885, p. 40. 



