16 



THE ART OF MAKING MICROSCOPE SLIDES 



Cements 



vals along the first and second shelves. 

 After a few moments it will be apparent 

 which point is just at the melting point 

 of the cement in question. The slide bear- 

 ing the small pieces in the position where 

 the objects are to be mounted is then 

 placed at this point and each object is 

 individually placed in its own little pool 

 of molten cement. It must be left at this 

 temperature long enough for the object 

 to reach the temperature of the cement 

 or it will not stick. It is best not to cool 

 these preparations suddenly, so that it is 

 the author's practice to take them from 

 the hot shelf on which the cement is 

 molten, remove them to the shelf under- 

 neath, and after they have cooled to that 

 temperature to place them on the bench 

 for their final cooling. 



For attaching opaque objects, particu- 

 larly those of relatively large size, nothing 

 is simpler than the wax-resin backgrounds 

 which have been mentioned. In using 

 these, a fairly thick coating is applied to 

 the warmed slide and the object dropped 

 into place. It is left until it has reached 

 the temperature of the cement, or the 

 cement is seen to be "creeping," and is 

 then cooled. These media are more fre- 

 quently employed by botanists for mount- 

 ing dried-spore cases of mosses, and the 

 like, but they also work admirably for 

 zoological specimens. 



Selection of Cement for Attaching the 

 Cover Glass 



Before discussing the selection of a 

 cement for the attachment of a cover glass, 

 which is the last step in the preparation of 

 a dry wholemount, it is necessary to insert 

 a warning that the word dry as applied to 

 dry wholemounts must be interpreted 

 literally. If wholemounts are being made 

 in an American laboratory in winter at an 

 inside temperature of 70°F. and an out- 

 side temperature around 0°F., no diffi- 

 culty will be encountered since the atmos- 

 pheric humidity is practically nil. If, how- 

 ever, the humidity is relatively high some 

 method of drying the specimen must be 

 used. The writer has in his possession 

 several imperfectly sealed dry whole- 



mounts of ground sections of bone, made 

 in Europe about forty years ago, which 

 are entirely covered with fungus hyphae. 

 The object may, it is true, be treated with 

 some fungicide but this is rarely as effec- 

 tive as, and usually more trouble than, 

 making sure that the mount is dry before 

 sealing. If the object has been attached by 

 one of the techniques which involves heat- 

 ing the slide and cement, it will probably 

 have dried sufficiently, but it is desirable 

 to make sure by leaving the uncovered 

 mount overnight in a desiccator over some 

 standard desiccant. 



When a coversUp is to be attached to a 

 gold-size or other cement cell, it is best to 

 use the same cement as was used in the 

 preparation of the cell. A thin coat of this 

 cement is applied to the top of the cell and 

 left until it becomes tacky. A clean cover- 

 slip is then placed on top and firmly 

 pressed into position with a needle. It is 

 easy to see whether adhesion is perfect 

 and, if necessary, a small quantity of 

 cement may be added from outside. It 

 must be emphasized that only a very thin 

 coat should be used because a thick layer 

 will inevitably run in by capillary attrac- 

 tion and thus ruin the specimens which 

 have been mounted. 



It is really not important what cement 

 is used when a coverslip is to be attached 

 to the top of a paper, cardboard, or plastic 

 cell. The author invariably uses gold size, 

 largely from force of habit, but any liquid 

 cement or varnish is adequate. A thin 

 layer is painted on the upper surface of 

 the cell and the coverslip pressed into 

 place. The preparation should now be 

 placed on one side luitil the adhesive is 

 dry, and then finished with a coat of some 

 black cement. Asphalt varnish [Benoit- 

 Bazelle (1942) is an excellent formula] or 

 Brunswick black (Beale 1880) both have 

 the required characteristics of providing 

 a waterproof seal while retaining a certain 

 amount of flexibility. These formulas, and 

 those of other suitable cements, are given 

 under V 12.2 in Chapter 28. The old seal- 

 ing-wax varnishes, and the modern cellu- 

 lose-ester varnishes have the disadvantage 

 that they tend to become brittle and break 

 ofT after some years. 



