Second Note on a Method of Preserving Rotatoria. 



By Charles F. Rousselet, F.R.M.S. 



(Read January 18th, 1895.) 



It is now just two years ago (" Quekett Journal," 1893, Vol. 

 v., p. 205) that I read before you a paper on preserving 

 Rotifers as permanent objects. Since then I have continued 

 my investigations, and have now made such progress and im- 

 provements in the method that a second communication on the 

 subject becomes desirable. 



The principle of the process, consisting of narcotizing, killing, 

 fixing, and preserving in a watery fluid, not appreciably denser 

 than water, as explained in my first note, remains the same, the 

 improvements being chiefly made in the details of the process 

 and the choice of the fluids. 



The first defect which became apparent was a darkening of 

 the specimens, due to the trace of osmic acid remaining in the 

 dilute Flemming's fluid used for preserving ; this was soon 

 remedied by omitting the osmic acid in the preservative fluid, 

 and the animals then kept their complexion very much better. 



The yellow colour, however, produced by the chromic acid in 

 some animals displeased me very much, as it gave an unnatural 

 appearance to the usually perfectly white, glassy transparent 

 bodies of Rotifers. I made many experiments with a number 

 of different substances to get rid of the chromic acid. The 

 most promising fluid for preserving seemed to be a J n per cent, 

 solution of bichloride of mercury, but owing to its liability of 

 forming crystals, which could not be wholly prevented by the 

 addition of a little common salt, I had finally to abandon it, ex- 

 cept in a few special cases. 



At the beginning of last year I noticed in the German 

 periodical "Biologisches Centralblatt" an article by Dr. Blumm, 

 on Formalin,* which was said to fix and preserve vertebrate 

 eyes and tissues without shrinkage and fairly transparent. I 



* Formalin, or formol, is a watery (40 per cent.) solution of formaldehyde 

 (CH 2 0), a gaseous substance which is produced when methyl alcohol is 

 subjected to oxidation. It is used as a disinfectant, and iustead of alcohol, 



