6O HOW TO WORK 



stance slightly thicker than the object with it between the glasses. A 

 little cavity may be made in many ways in which a specimen, dry or 

 with its preservative fluid, may be placed, and afterwards covered with 

 thin glass without risk of injury from pressure. This is termed a cell. 

 Cells may be composed of various materials according to the 

 thickness which may be necessary, and according to the nature of 

 the substance to be placed within them. 



114. Paper tells. For dry objects an efficient cell is readily made 

 with a ring of paper or cardboard fixed with gum to the glass slide ; 

 or a hole may be punched out of a piece of cardboard, wood, mill- 

 board, or gutta percha, or a vulcanized India-rubber ring may be 

 cemented to a slip of glass. Many other devices will occur to the 

 mind of any one who wishes to make neat cells of this kind. If, 

 however, the cell is intended to contain fluid, it must be made of 

 some substance impervious to moisture. 



115. Shell-lac Cells. Dr. Maddox recommends Bell's cement 

 thickened with crushed shell-lac dissolved in a very small quantity of 

 methylated spirit for making thin cells. 



The clean slide is warmed and placed on the " turn-table," 116, 

 pi. XVI, fig. 91 ; a fitll brush of the thickened cement is then made 

 to strike a circle. The slide is held over the spirit lamp until bubbles 

 are given off, when it is placed horizontally on a warm surface to 

 dry ; when nearly set hard it is removed, allowed to cool a little, and 

 a piece of thick plate glass, previously wetted, is pressed carefully on 

 the circle of cement until fastened equally. These cells can be kept 

 ready for use of various thicknesses. If the object be mounted in 

 glycerine in one of these cells, and is not likely to be injured by a 

 slight heat, it is best after placing down the thin cover and cleaning 

 the edges carefully, to gently warm the slide and press the cover 

 equally on the cement. If properly managed the cover generally 

 adheres to the cement, and after being cemented with a thinner solu- 

 tion of the same cementing medium forms an excellent close cell for 

 glycerine, 



HG. Brunswick Black Cell. A very thin cell may be made by 

 painting a ring of Brunswick black or gold size upon the glass slide, 

 and then allowing it to dry. 



The best form of Brunswick black cell is the circular one, which 

 is so easily made by the aid of Mr. Shadbolt's excellent turn-table, 

 pi. XVI, fig. 91. The slide is placed on the little brass wheel which is 

 made to revolve, while a brushful of Brunswick black is held at the 

 proper distance from the centre, according to the diameter of the cell 

 required. If a thick layer is desired the slide may be warmed, when 

 the layers of Brunswick black applied, dry very quickly. 



