Mounting Rotifers end Protista in Balsam. By E. Tozer. 25 



fixed by osuiic, cocaine, or picric— I put on the cover-glass, placing 

 a thread of white cotton between the cover-glass and slide, thus 



Fig. G. 



The cotton prevents the specimens from being crushed or washed 

 away in subsequent operations, and enables us to pass them through 

 all kinds of treatment. 



I now draw off the water by placing bits of blotting-paper to 

 the right of the cotton-thread, and apply osmic at the left of the 

 cover-glass. 



When the specimens are immersed in the osmic, add the stain, 

 picro-carmin or eosin. These two stains prevent osmic from 

 blackening, and the picro-carmin along with osmic differentiates 

 the structure. Staining and hardening are thus combined. 



The slide is then put in a dark moist chamber, to prevent 

 evaporation. I use two saucers. In the lower one I put some 

 water, and over it a square piece of glass. The slide goes on the 

 glass, and the whole is covered with the other saucer, which is 

 moistened. 



Time required for hardening varies with different forms. 

 Brachionus will be ready for further treatment in 5 hours; 

 Htjdatina, 12-24 hours ; CEcistes, 24 hours ; Floscularia (whose 

 case is so difficult to fix), 3 days ; amcebce and other allied forms, 

 about 10 hours (the latter with picric method). 



When hardening is complete, the specimens must be washed. 

 Elotting-paper is applied to the right of the cotton, and drops of 

 water to the left side of the cover-glass. After all the osmic and 

 stain are washed out from under the cover-glass, leave the specimens 

 in the water some fifteen minutes. I often counter-stain here with 

 eosin, which expels acid. Now thoroughly dehydrate with absolute 

 alcohol, applying drops and blotting-paper. After thoroughly 

 Mashing with this alcohol, leave the specimens in it for at least 

 one hour, to clear all trace of acid. Any acid present causes 

 shrinkage when oil is applied. 



I next apply oil of cloves, the worst possible oil for many 

 things, but excellent for Rotifers mb Protista prepared as described. 

 The oil is applied in the same way as the water and alcohol. I 

 leave the specimens in the oil for half-an-hour. As this oil d 

 not evaporate, the cover-glass may be lifted and the specimen 



