176 SERIAL SECTION MOUNTING. 



In the Journ. Roy. Mic. Soc. (N.S.), vol. ii, 1882, p. 888, it is stated (on 

 whose authority is not clear) that the solution is made by mixing 1 part of 

 bleached shellac with 10 parts absolute alcohol, and filtering. In the same 

 place it is added that " Dr. Mark uses the bleached shellac in the form in 

 which it is prepared for artists as a ' fixative ' for charcoal pictures. It is 

 perfectly transparent, and a film of it cannot be detected unless the surface 

 is scratched. He attaches a small label to the corner of the slide, which 

 serves for the number of the slide and the order of the sections, and at the 

 same time marks the shellac side otherwise not distinguishable." (The 

 latter object is better attained by gumming a paper square, or spinning a ring 

 with ink, in the centre of the unprepared surface of the slide. The disc or 

 ring then serves at the same time for centering the group of sections. 



The account given in the Mitth. d. Zool. Stat. further varies in one other 

 detail from that given in the Zool. Anz. It directs that the shellac slides 

 be brushed before cutting with oil of cloves, instead of kreasote, the slide 

 being slightly warmed before brushing. 



The white shellac of commerce is sometimes not easily soluble in alcohol. 

 KINGSLEY (see WHITMAN'S Methods in Microscopical Anat., p. 117) recom- 

 mends that brown shellac be taken and bleached by exposure to the sun. 



CALDWELL (Quart. Journ. Mic. Soc. (N.S.), Ixxxvii, 1882, p. 336) 

 simplifies the method by merely brushing over the slide (thinly) at the 

 moment of using with a strong solution of shellac in anhydrous kreasote. 

 (To make the solution, warm the kreasote.) 



In both the foregoing methods it often happens that the shellac becomes 

 granular or cloudy on the slide. P. MAYEE attributes this to the kreasote 

 or clove oil, and proposes to remedy it by employing carbolic acid instead 

 (Amer. Natural, 1882, p. 733; Zeit. f. \viss. Mik., iv, 1, 1887, p. 77); 

 Journ. Roy. Mic. Soc., 1885, p. 910). Powdered white shellac is -heated 

 with crystallised carbolic acid till it dissolves, and the solution filtered 

 warm. 



But more recently (Intern. Monatschr. f. Anat. c., 1887, H. 2 ; Zeit.f. 

 wiss. Mik., iv, 1, 1887, p. 77) the same author, on the ground that hot car- 

 bolic acid attacks some tissues, recommends another method. Slides are pre- 

 pared with alcoholic shellac according to Giesbrecht's plan. The sections 

 are arranged on the dry film and gently pressed down on to it, then exposed 

 for half a minute to vapour of ether. 



Chloroform softens shellac ; therefore, chloroform balsam is not a safe 

 mounting medium for sections fixed by these methods. 



These methods do not allow of staining on the slide. 



I feel bound to say that I am at a loss to understand by what virtue 

 it is that the shellac method continues to survive, as it certainly seems to do, 

 in the face of far more convenient and efficient processes. 



318. Mayer's Albumen (Mitth. Zool. Stat. Neapel, iv, 1883; 

 Journ. Roy. Mic. Soc. (N.S.), iv, 1884, p. 317; Internat. 

 Monatschr. f. Anat., 1887, Hft. 2; Journ. Roy. Mic. Soc., 1888, 

 p. 160). White of egg. 50 c.c., glycerin, 50 c.c., salicylate 



