786 



PEEPAEATION OF CELLS. 



The asphalte is applied by means of a hair pencil, the slide being 

 placed on a turn-table (fig. 954), which has circular marks on it corre- 

 sponding to the required dimensions of the cavity. The depth of the 

 cavity can be varied according to circumstances, by putting one or 

 more layers of asphalte. After the thin glass cover is put on, it is luted 

 carefully with asphalte. The cavity is filled with distilled water, weak 

 pyroligneous acid, alcohol, diluted glycerine, 

 a very weak solution of creazote (one drop 

 to the ounce of distilled water), or some 

 other fluid. When specimens are very 

 minute the asphalte cell is not required; 

 the thin glass is applied at once to the slide, 

 a drop or two of the fluid being ioserted 

 along with the specimen. In the case of 

 some dry preparations, as pollen-grains and 

 the fine-lined Diatoms, no fluid whatever 

 is required, but precautions must be taken 

 against the access of damp. Canada balsam 

 is useful in some instances. The specimen 

 is laid on a slide,'then a drop of the solution 

 of Canada balsam is put on it, and the thin 

 glass above all. It is then set aside to dry, 

 and ultimately a rim of asphalte is made 

 round the margin of the glass cover. Canada 

 balsam is well fitted for many Diatoms, and for thin sections of 

 woods. In putting up woods, the specimen is placed in the centre 

 of the slide, a drop of turpentine is insinuated below it, with a camel- 

 hair pencil, in order to expel the air ; a solution of Canada balsam is 

 then applied, and the same procedure is followed as above. 



To MAKE Cells, and to fix the thin Glass Covers. — The 

 cells are made either round or square by thin layers of cement, according 

 to the depth required. Perhaps the round ones are neater, but they 

 require circular pieces of glass for covers, and by the aid of the turn- 

 table (fig. 954) the roundness of the mounting can be made with perfect 

 accuracy. The cover is laid gently down, so as to float on the solution 

 in which the object lies, and by pressing carefuUy on the cover, the 

 superabundant fluid is made to pass out by the edges, and may he 

 taken up by blotting paper. A thin layer of asphalte, or gold size, 

 may be placed round the edge, which wiU gradually harden and 

 completely seal up the preparation. 



Fig. 954. Ttim-table for making the circular rim of asphalte ; b, a piece of mahogany ; tf, a 

 circular piece of brass, which can be moved, round by the hand, and has two brass springs 

 on its surface for holding a glass slide firm. In the centre of the brass disc are circular 

 markings fitted for the size of asphalte cells required. These marks being seen through the 

 slide laid above them, guide the hand in making the circular asphalte rim, the brass disc 

 being turned round during the application. 



Fig. 964. 



