G C. tf. ROUSSELET ON PRESERVING ROTATORIA. 



procured some of tin's substance, and soon perceived that it 

 would be very useful for my purpose. Formalin by itself, I find, 

 does not fix the Rotifers at all well, as I was led to expect from 

 the above article ; it rather dissolves protoplasmic structures, 

 such as cilia, more or less completely, but it preserves them re- 

 markably well after they have first been fixed with Flemming's 

 fluid or osmic acid, and crystals are never formed. It has the 

 very valuable property of preserving the animals without the 

 least shrinkage or turgescence, and as perfectly transparent as 

 the fixing process leaves them. The thin and delicate loricaof 

 some Rotifers, such as that of Euchlanis triquetra, which I had 

 not been able to satisfactorily preserve in any other fluid tried, 

 remains perfect in shape and transparency in formalin. The 

 strength used is 2| per cent, in distilled water. 



For fixing the Rotifers I have found that osmic acid alone 

 fixes as well as Flemming's fluid ; when used strong it darkens 

 the animals, but if a very weak solution of \ per cent, or less be 

 used, and allowed to act for a very short time only, half a 

 minute at most, the animals remain white and transparent, ex- 

 cepting only the maturing ova, which become more or less 

 darkened on account of the fat-like substance, lecithine, which 

 they contain. Moreover, if the animals have become coloured 

 a little by the osmic acid the colour can be removed by passing 

 them for a few (1-3) minutes through peroxide of hydrogen.* 



For narcotizing I found the following mixture to give better 

 results than 2 per cent, cocain alone : — 



2 per cent, solution of cocai'nf ... 3 parts 

 Methylated spirit £ ... ... 1 ,, 



Water 6 „ 



for preserving museum specimens, is non-poisonous, and very cheap. The 

 solution obtainable in commerce being of thestrength of 40 per cent., dilute 

 2g volumes of this with 374 volumes of distilled water in order to get the 

 required solution of 2\ percent. 



* Peroxide of hydrogen is simply water containing an excess of oxygen, 

 either in loose combination or only in solution, or more probably both'; the 

 oxygen is readily given off and bleaches by oxidizing the reduced osmic 

 acid to OsO 4 . This substance does not keep good very long, and it is best 

 to obtain a small quantity at a, lime and renew it after four or six months. 



f Hydrochlorate of cocain is a very expensive drug; it is best to procure 

 only one gramme at a time, and dissolve it in 50 c.c. of water, which will 

 give a 2 per cent, solution. As this solution does not keep well I add at 

 once 12 c.c. of methylated spirit, then four parts of this mixture and six 

 parts of water will make the above narcotizing fluid. 



X I mean the methylated spirit prepared with wood naphtha, not that now 

 generally sold, which is prepared with mineral naphtha, and becomes milky 

 ■vhen mixed with water. 



