l888.] NEW-YORK MICROSCOPICAL SOCIETY. 11 



glass should be put on before the balsam is added as it prevents 

 the specimen from again becoming coiled or displaced. A 

 drop of balsam in benzole is put adjacent to the edge of the 

 cover, and the slide held an instant over a gas burner or alcohol 

 lamp, which will cause the balsam to flow by capillarity under 

 the cover-glass. A small spring-clip is then used to press the 

 covei" down and hold it in place. The slide is removed to a 

 drying oven, and left until the balsam has hardened, so that the 

 portion outside the cover can be scraped off. The slide is then 

 cleaned by washing in strong alcohol, using a piece of soft tissue 

 paper to rub it dry. It is quite essential to use cover-glasses of 

 known thickness. Many radulae require a one-tenth inch objec- 

 tive. The convexity of the object combined with the thickness 

 of the cover, necessitates the use of very thin glass. For the 

 Rissoidce, I have usually employed glass of .004 inch thickness. 



The finishing and labelling of the slide are matters of indi- 

 vidual taste, and are not requisite to the success of the prepara- 

 tion, except that the cover must not be piled high with varnishes 

 and cements, which will interfere with the use of high magnify- 

 ing powers. My usual method is to run a small ring of shellac 

 around the edge of the cover, and, in case of bad centering, or 

 other slight defects of mounting and cleaning, or often for pure 

 ornament, to add colored rings with a very fine brush. The 

 colored varnishes are composed of the best tube oil colors, dis- 

 solved in chloroform and reduced with balsam in benzole ' 

 These colors are translucent, permanent and ornamental. 



The advantage of using an erector, for delicate manipulations 

 under the microscope, cannot be overestimated, as the best suc- 

 cess can thus easily be obtained. We may learn to use one hand 

 in reversed movement, but it is almost impossible to govern 

 both hands, so that these delicate objects may be safely handled. 



Some good preparations were obtained by substituting nitrate 

 of silver for the chromic acid, as a staining reagent ; but the 

 specimens require boiling in the silver solution, and this addi- 

 tional step further complicates the process, and makes it less 

 possible to retain small specimens. Besides, too much action 

 of the silver renders the objects opaque. 



In conclusion, I may say that with rare and minute species of 

 shells, the entire sequence of steps, in the preparation of the 

 radula, may be performed upon the slide, with the assurance 

 that the object cannot easily escape. 



