88 SPECIFIC EXAMPLES OF SLIDE-MAKING 



making a pousse-cafe) in order to float a layer of alcohol on top of the terpineol. 

 The specimens are now dropped into the alcohol. Naturally they sink through 

 it, coming to rest on the surface of the layer of terpineol into which they sink 

 slowly without any strong diffusion currents. They will be seen to have sunk 

 to the bottom after a little while, but there will still be a quantity of alcohol 

 diffusing upward from them. As soon as these diffusion currents have ceased, 

 the alcohol should be drawn from the top of the tube with a pipette and the 

 specimens transferred to clean terpineol. When they are in fresh terpineol, 

 they should be examined carefully under a microscope to make sure that they 

 are glass-clear without the least trace of milkiness. If they appear slightly 

 milky, they have either been dehydrated insufficiently or the alcohol used for 

 the preparation has become contaminated with water. In either case they must 

 be transferred to a tube of fresh alcohol for complete dehydration. Then they 

 are transferred back into terpineol in the manner described. It is a sheer waste 

 of time to endeavor to prepare a balsam mount from a specimen which is not 

 perfectly transparent in the clearing medium. 



When all the specimens are in natural balsam, one should have ready some 

 clean slides, some clean M-in. circular coverslips, and a balsam bottle contain- 

 ing natural balsam. The author's preference for the natural balsam rather than 

 a solution of this material in some solvent has been explained previously (see 

 p. 46). For example, a drop of the natural balsam is placed on each of six 

 slides, and then, one at a time, six specimens are lifted from the terpineol and 

 placed on top of the balsam. The specimens will sink through the balsam very 

 slowly, so that these six slides should be pushed aside while the next six slides 

 have drops of balsam put on them, and so on. As soon as a specimen has sunk 

 to the bottom of the drop of balsam, a coverslip is held horizontally above, 

 touched to the top of the drop, and then pushed down with a needle until 

 the specimen is flattened firmly against the slide. Since these specimens have 

 been properly hardened and flattened, there is no risk of their being damaged 

 by drying the mount under pressure, so that a clip can be applied (see Fig. 12) 

 and the slides placed on a warm table to harden. Each is cleaned, finished, 

 and labeled in the manner suggested previously (see p. 75). 



Summary 



1. Narcotize with menthol. 



2. Kill with 4 per cent formaldehyde. 



3. Harden selected polyps compressed between slides in 95 per cent alcohol. 



4. Stain 1 to 24 hours in Grenacher's alcoholic borax carmine. 



5. Differentiate in acid 70 per cent alcohol until pink. 



6. Dehydrate, clear in terpineol, and mount in balsam. 



