76 MATERIALS AND PROCESSES OF SLIDE-MAKING 



removed is scraped off with a dull knife. A small lump of absorbent cotton 

 saturated in 96 per cent alcohol is used to rub off the remainder of the resin. 

 It is not safe to endeavor to clean a balsam slide with benzene or xylene, for 

 the coverslip will be loosened inevitably by this method. As soon as the sur- 

 plus resin has been dissolved away, the slide is dipped immediately into a 

 warm soap solution and then polished. This leaves a very brilliant finish and 

 an entirely clean slide. 



An additional reason why slides should always be washed in soap and water 

 after they are mounted is because there is no known method by which a gummed 

 paper label may be made to adhere to greasy glass. More slides are rendered 

 useless through the loss of their label than from any other defect. Almost 

 everyone today buys pregummed paper labels, so that it is scarcely worth while 

 in this text to give formulae for label adhesives. There is, however, a very 

 definite technique by which the label may be made to stick most readily. This 

 is to lick the upper surface of the label, moisten thoroughly the lower surface, 

 and then, when both sides are fully expanded, to press it firmly on the glass. 

 Labels attached in this manner have remained for more than 20 years in 

 the author's collection without becoming detached. One may either then 

 wait until the label is dry before printing neatly on it with waterproof 

 India ink the name of the specimen or, if one is dealing with a large series 

 of slides, one may write the label first in waterproof India ink and, having 

 left it at least 24 hours to dry, attach it by the method indicated. 



Even if the label is attached by the method indicated, it is always best, in 

 the case of valuable slides, to write a brief label with a writing diamond on 

 the glass underneath the label. 



There is only one absolutely permanent method of labeling a microscope 

 slide, and that is to use a slide of which about an inch at the end has been 

 ground to a rough surface. After the slide is finished and cleaned, the label is 

 written on this ground surface either with a soft pencil or with waterproof 

 India ink. Then a drop of balsam is placed on the label before attaching a 

 coverslip over the the surface of it. The objections to this method are that it 

 is very expensive— the slides cost four or five times as much as ordinary slides 

 —and also that there is a grave risk that the coverslip will be broken by some- 

 one placing the clip of the microscope stage on top of it. 



The proper storage of microscope slides is just as necessary as proper label- 

 ing. Slides should always be stored in the dark and in as cool a place as pos- 

 sible because none of the stains used in biology are absolutely permanent. 

 Slides may be stored either vertically on edge in grooves in a tray of a cabinet 

 of the type shown in Fig. 56 or lying flat on the bottom of a tray as in the 



