MICROSCOPICAL TECHNIQUE. 427 



of celluloid. This is easily done if the material be laid on a thick 

 and smooth block of lead, and the punches be kept sharp. Mois- 

 tening the surfaces of the rings with a mixture of alcohol and ether 

 (or absolute alcohol will answer) until a ring of sufficient thickness 

 was built up, the composite ring was placed under a weight and 

 allowed to dry. In the cells intended for specimens for direct 

 examination, the bottom was formed of a disc of celluloid of the 

 same external diameter as the rings, and the rings were then 

 cemented to it. The internal diameter of the upper ring of the 

 series was made about one-tenth of an inch larger than its fellows, 

 in order to form a seat for the cover-glass. The roughness was 

 removed from the external portion of the cell by placing the slip 

 to which it was cemented on the turn-table, and revolving it first 

 against a file and afterward against a bit of crocus-cloth, cemented 

 to a smooth piece of wood. Finally, a high polish was given by 

 rotating the ring against a little silk pad, wet with absolute alcohol, 

 and then rubbing it with silk greased with olive oil. When 

 finished, the cell resembled one turned from solid ivory. After the 

 cells were filled with material, they were closed by dropping the 

 cover-glass into the recess prepared for it, the edges of which were 

 touched with absolute alcohol before dropping the cover-glass into 

 place. The operation was finished by cementing a final ring of 

 celluloid so as to cover the joint made with the glass. The cells 

 thus made, while apparently tedious to prepare, are very handsome, 

 and do not actually take much time to construct. It will not do 

 to use alcohol and ether mixture to fasten the cells to the slip. 

 The joint, while perfect at first, soon separates, and the cells drop 

 off the glass. White zinc cement, diamond cement, or marine glue, 

 makes a firm joint. The alcohol and ether mixture, however, 



makes a firm joint of celluloid to celluloid For the 



reason given, it is best to fasten the cover-glass to its seat (if an 

 air-tight joint is desired) with gelatin or any of the cements 

 mentioned." 



Balsam-paraffin for Cells .■^— Dr. A. A. Juhen observes that 

 the mixture of balsam and paraffin for making cells deserves to be 

 better known. Balsam cement is first prepared by slow evapora- 



* Journ. R. Alicr. Soc. (1893), p. 567, from Jour?!. New York 

 Alter. Soc, IX. (1893), PP- 39—43- 



