The Microscope. 175 



that the specimen be more completely dehydrated, and then it often- 

 times renders it too transparent and always too brittle. On the 

 other hand, it is colorless and very cheap. The beginner is advised 

 to practice with turpentine, as at small cost large quantities can be 

 used, thus facilitating the manipulation of the object. 



Now carefully cleanse a slide — or "slip," as it is more properly 

 called — and a cover-glass. By this time the specimen will have 

 been made sufficiently transparent and ready to mount. On a fresh 

 paper the size of the first one used, and with a fine eamel's-hair 

 pencil, arrange the object. Draw it carefully from the medium and 

 touch the paper lightly to a blotter to remove the suparfiuous oil. 

 Now lay it gently on the center of the slip,- paper uppermost. 

 Without releasing from the forceps the paper can generally be 

 peeled off, leaving the specimen behind nicely arranged and in 

 order. If the paper sticks, a little urging may loosen it, being 

 •careful not to move the object from the center of the slip; if not, 

 then lay aside the forceps and gently press a blotter on the paj^er, 

 thus fixing the specimen to the slip and removing much of the oil 

 which holds it to the paper. A needle-point inserted under the 

 edge of the paper will now turn it up, that it can be grasped and 

 removed. Now add two or three drops of the chloroform-balsam 

 and put on the cover- glass as described in the second lesson of 

 these papers. Press the cover down so it fits evenly and set away 

 to dry. 



If too much balsam be used, it will exude at the edges of the 

 cover. This can be scraped away when dry. If too little be 

 employed, more should be added at once by touching a drop to the 

 edge of the cover. Capillary attraction will carry it under. With 

 practice, however, it will be possible to judge of the exact amount 

 required to fill out nicely. It will be well for the first few days 

 after mounting to examine the slide carefully to detect shrinkage of 

 the balsam. If vacuolations are found they should be filled with 

 balsam as above described. 



In balsam-mounts included air-bubbles should create no con- 

 cern, as they usually pass ovit without treatment. This fact, how- 

 ever, is no excuse for carelessness in allowing the bubbles to form. 



The specimen is now finished, and when labeled and kept from 

 the dust and light will endure almost forever. 



In the writer's opinion, Canada balsam is the best medium for 

 permanent mounts. True, glycerin is often necessarily employed 

 for very delicate specimens or those which have been stained with 

 certain dyes. But such mounts are hardly as permanent, though 



