422 MICROSCOPICAL TECHNIQUE. 



with the hands, all the soluble or very finely suspended particles 

 are washed away through the texture of the bag. The clean residue 

 is then placed in a large flat dish of water and stirred round, when 

 the fine floating organic portion, often very rich in Foraminifera, 

 Diatomacea^ Ostracoda, Amphipoda, etc., can be strained off and 

 placed in a preservative fluid for examination. 



Method of Preserving Rotatoria."^— Mr. C. F. Rousselet 

 having made many experiments in order to preserve the rotifers, 

 says the following method has proved very successful in his hands. 

 The process consists of four stages, viz., narcotising, killing, fixing, 

 and preserving. 



Narcotising. — A fluid eminently suitable for this purpose is a 

 watery solution of i to 2 per cent, of hydrochlorate of cocain. A 

 small quantity of this solution, added to the water in which the 

 rotifers are, does not at first afl'ect them, but, after some minutes 

 (5 to 15), their motion becomes slower, and, in successful cases, 

 they finally sink to the bottom of the trough fully extended, with 

 the cilia vibrating but feebly. It is necessary to watch them until 

 the cilia have just ceased to vibrate, and then, in the majority of 

 species, is the right moment to kill. The action of cocain varies 

 greatly in different rotifers,, so that experience is necessary to be 

 able to judge as to the right quantity required. 



Killing and Fixing.— Both these operations are performed 

 simultaneously by adding a small quantity of Flemming's chromo- 

 aceto-osmic acid mixture (15 parts of i per cent, chromic acid, 

 4 parts of 2 per cent, osmic acid, i part of glacial acetic acid). 

 The animals remain in the fixing solution a quarter to half an 

 hour, not longer ; small rotifers rather less. The solution is then 

 washed out with distilled water by changing the water five or six 

 times. 



Preserving. — Mr. Rousselet finds that the best preserving fluid 

 is simply distilled water rendered antiseptic by a trace of the 

 fixing solution (8 drops to i oz. of water). 



Nature of the Staining Process of Vegetable Tissues.!— It 

 has long been a matter of controversy whether the colouring of 



* Journ. Qtiekett Micr. Chih, II., v. (1893), PP- 205 — 209. 

 t Dingler's Polytechn. Jotirn., 1893, Heft 9. 



