ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 735^ 



until we have a membrane of about 1 mm. thick. The hairs are thus 

 fixed so that they cannot move whatever may be done with the layer of 

 collodion. 



When dry the sections are cut in the Lelong microtome {supra, 

 p. 733). All that is necessary is to cut out of the plate of collodion a 

 square of about 1 cm., and to inclose it between a small piece of soft 

 wood and some elder-pith. We thus obtain small plates of collodion 

 containing sections of the hairs absolutely perpendicular to their 

 greater axis, and these can be mounted in glycerine or better in Canada 

 balsam, but in the latter case, oil of cloves must be avoided, which 

 would dissolve the collodion and free the sections, allowing them to 

 lose their horizontal position. 



By this process the author has been able to demonstrate in the 

 clearest manner the torsion of the hairs of the negro. The hairs being 

 fixed in the collodion a small piece of cork cut in the form of a rect- 

 angular triangle is fixed to the slide and the sections are made by 

 cutting both the cork and the collodion. It is thus possible to orient 

 them all in the directions which they took originally. The great axis 

 of a section is first observed, and a little afterwards we come upon one 

 whose direction is at right angles to the former, which demonstrates the 

 torsion. From the examination of a great number of sections the 

 author has been able to establish how much the forms vary with 

 the different races and he thinks it will perhaps be possible by the 

 measurement of different diameters to establish a special classifica- 

 tion. 



Fixing Sections.* — Dr. J, Frenzel, referring to his former paper f 

 and that of Mr. E. Threlfall | recommending caoutchouc instead of 

 guttapercha, says that the former substance has certainly the advan- 

 tage of giving more quickly a serviceable solution with the solvents 

 used (chloroform or benzine), and the layer spread on the glass dries 

 more quickly than guttapercha ; but the latter has the more important 

 advanteiges, (1) of adhering better, as it never quite dries and softens 

 with heat ; and (2) of dissolving less quickly in the common solvents, 

 especially in naphtha, and is therefore considerably more resisting than 

 caoutchouc. 



A remarkably good guttapercha solution (1 : 100) can be obtained 

 of Beyrich of Berlin. To prepare the solution oneself, the filtrate 

 must be left to stand from two to three weeks, frequently well shaken, 

 and finally filtered from the deposit. The solvent suggested by 

 Threlfall — naphtha or parafSn oil — is on the contrary. Dr. Frenzel 

 considers, very useful and satisfactory in every respect, at least as far 

 as regards the former, which alone he has tried. Threlfall has, how- 

 ever, he considers, described the mode of operation so insufficiently 

 that few will succeed in obtaining a good result with this method. 

 Dr. Frenzel therefore gives his method. 



After the sections are arranged on the dry adhesive layer, the 

 slide is warmed for a short time to (at the most) 50° or 55° C, for which 

 a few seconds are sufficient and even a considerably lower tempera- 



* Zool. Anzeig., vi. (1883) pp. 422-4. 



t See this Journal, ante, p. 307. % Ibid., p. 600. 



3 c 2 



