Mounting Rotifers and Protista in Balsam. By E. Tozer. 27 



prepared on the cover-glass. The cover-glass is smeared by a 

 brush dipped into, let us say, a swarm of Chlamydomonas. Drop 

 on a little osmic acid, and add picro-carmin. Leave it thus in the 

 moist chamber for '24 to 48 hours. When taken out, allow the liquid 

 to nearly evaporate until the cover-glass is seen to be just moist. 

 Now turn over the cover-glass on to a slide, interposing the thread 

 of cotton. 



It will be found that most of the forms are fixed on to the 

 cover-glass. Wash very gently with water, then alcohol, as 

 described for Rotifers. Then follows the oil, and the cover-glass 

 is lifted on to a drop of balsam on a clean slide. This method 

 shows both structure and cilia. 



Many very minute Protista may be mounted by the ordinary 

 methods of preparing blood. The best fixative is formalin vapour. 

 Moisten a cover-glass, and it will fix to a flat-shaped watch-glass. 

 Turn this over on to a deep watch-glass containing formalin. 

 Leave on a warm place for 15 minutes. 



The specimens are fixed. They may be dried and stained as 

 witli the blood method, or, better, passed through the processes 

 described for Chlamydomonas. For these processes they will 

 require longer fixing. 



A word on mounting Hydra viridis may be useful. Put the 

 specimen on a slide in water with cover-glass and cotton. Let it 

 extend naturally. Apply the smallest possible quantity of abso- 

 lute alcohol, letting it reach the animal at its base, where it is 

 least sensitive. 



It will stretch and die. Dehydrate at once, and let it harden 

 in absolute alcohol for an hour or so. Replace the alcohol with 

 water to stain. Stain with picro-carmin 1 hour, counter-stain 

 with Heidenhain's hematoxylin 15 to 30 minutes, wash, dehydrate, 

 apply the oils, mount in balsam. 



If in any of the above methods absolute alcohol should give 

 any trouble, use the graded alcohols, 3<> p.c, 60 p.c., then ( .»0 p.c., 

 then absolute. 



The advantages of balsam mounts need scarcely to be stated ; 

 they allow the" best methods of staining; when stained, the 

 specimens exhibit structure more clearly than by any other 

 methods. And then, of course, the mounts are permanent. 



I would advise workers to experiment first with Brachionus, 

 because of the firm envelope. 



For extremely delicate forms I have recently tried with succ* 

 the following method. After extending, hardening and washing as 

 described above, I have put the specimens through a second pro- 

 cess. I lift the specimens into a few drops of osmic and leave 

 them 2 to 4 hours. Then I wash with water, dehydrate, add the 

 oil, and then balsam. 



