58 On an improved Method of Making Microscopic Sections. 



laboratories for aid, neither glass, nor iron, nor hemp, nor 

 adamant itself, will suffice to defy them. If any material exists, 

 the characters of which are so thoroughly dissimilar from those 

 of any substance known to occur at the bottom of the sea as to 

 render it in the highest degree improbable that such creatures 

 as live there could improvise means to pierce it, whilst, at the 

 same time, it would secure perfect insulation of the telegraphic 

 wire, caoutchouc is that material. 



VI, — Improved Method of making Microscopic Sections. 

 By G. C. Wallich, M.D., F.L.S. 



To the Editors of the Annals and Magazine of Natural History. 



Gentlemen, 



Having devised a method of producing the finest sections of 

 minute microscopic objects, such as Foraminifera, Diatomacese, 

 and the like, which will, I think, prove of great service, I beg 

 leave to lay it before your readers. 



Hitherto, in making sections of any minute organized parti- 

 cles, the practice has been to mix the material with Canada 

 balsam hardened over the spirit-lamp in the usual manner, and 

 to grind down the balsam and its contents on a glass slide, 

 until of the requisite degree of thinness, — a thin glass cover 

 being placed on the ground surface, in order to complete the 

 Operation. 



This plan, however, possesses the great disadvantage of afibrd- 

 ing only one ground side for microscopic examination, namely 

 the one next to the observer's eye ; whilst, the surface next the 

 glass slide being in its natural state, not only is perfect defini- 

 tion prevented, but it is impossible to ensure anything like a 

 uniform thickness of the various minute sections present. 



To obviate this defect, I simply substitute, for the glass slide 

 employed in the early stage of the process, a thin film of mica, 

 mixing the material to be operated on with the balsam, and 

 hardening it by heat in the usual mode. The slip of mica so 

 prepared is now transferred to a glass slide, and secured by 

 balsam as before, the mica being next to the glass. The opera- 

 tion of grinding down the exposed surface having been carried 

 to the desired limit, and the surface carefully washed with 

 water in order to carry off" all loose particles, heat is applied 

 to the under surface of the slide in order to drive off" the last 

 remnant of moisture left from the process of grinding-down. 

 The slide is then heated just sufficiently to admit of the detach- 

 ment of the mica-film and its burden in situ. A clean slide is 

 now gently heated, and the mica-film, with its balsam-surface 



