34 



THE ART OF MAKING MICROSCOPE SLIDES 



Sealing 



for the escape of the heated glycerol. 

 The slide is then cooled, such glycerol as 

 has been extruded from the corner is 

 wiped away, and a small drop of very hot 

 cement is apphed at this place. Slides 

 sealed in this manner will last almost 

 indefinitely and require no further finish- 

 ing beyond a brief wash in alcohol to 



slip. The size of the drop is therefore 

 critical but can onlj^ be learned by 

 experience. 



The shde is now placed on a warm 

 table, kept a few degrees above melting 

 point of the petrolatum employed, and 

 molten petrolatum run under the cover 

 from a pipet. Spence prefers to take a 



Fig. 20. Sealing a wholemount with Fant's cement. 



remove excess glycerol. They are, how- 

 ever, clumsy in appearance compared to 

 a ringed slide made with dichromate 

 gelatin. 



Sealing Glycerol Mounts with Petro- 

 latum 



This method, which was developed by 

 Spence 1940 {Microscope, 4:123) is the 

 best yet developed, providing one is 

 looking for chemical stability rather than 

 mechanical strength. The object is lifted 

 in a drop of glycerol and placed in the 

 center of a clean shde. Three Uttle squares 

 of petrolatum-soaked paper or card, of a 

 thickness sufficient to prevent coverslips 

 crushing the object, are placed round, but 

 not in contact with, the drop. The cover- 

 slip is now lowered vertically onto the 

 drop which should spread out, when the 

 coverslip is resting on the squares, until it 

 occupies about half the area of the cover- 



wisp of solid petrolatum on a toothpick 

 and to let this melt and run under the 

 covershp. In either case, one is left with a 

 bubble of glycerol surrounded by a thick 

 layer of molten petrolatum. The slide is 

 now chilled and any excess petrolatum 

 scraped away. The mount is permanent 

 in this form, but the petrolatum is so 

 soft that the cover is liable to become de- 

 tached when dust is wiped from it. A 

 certain degree of mechanical strength can 

 be given by turning on three or four rings 

 of shellac, followed by three or four coats 

 of asphalt varnish. 



Sealing Other Non-aqueous Liquid 

 Mounts 



Mounting in liquid petrolatum is prac- 

 tically confined to blood films, on the 

 assumption that this inert medium pre- 

 vents the fading of methylene blue-eosin 

 stains. These stains are, however, best 



