320 C. F. ROUSSELET OX 



lac manufacturer to prepare his cement so that it may always 

 be obtainable at a reasonable price and in small quantities.* 



The glass micro-cells require a further word. At first I had 

 great difficulty in obtaining suitable sunken glass slips. The 

 first specimens w^ere obtained from Birmingham, but the polish- 

 ing of the cavities was so rough and faulty that I gave them 

 up. After a time I discovered a firm in Hanover f where I 

 could obtain everything I required. Opticians here used to 

 charge me 2d. each for very inferior glass slides, but from tliis 

 firm I was able to obtain them finely polished at a wholesale 

 price costing less than IO5. a hundred. 



Some years ago I also gave considerable attention to fresh- 

 water Polyzoa. My method of narcotising, fixing and mounting 

 has been fully described, with some additional methods of his 

 own, by Mr. H. E. Hurrell, F.R.M.S., of Great Yarmouth, in 

 the Micrologist, part 2, vol. iii., January 7th, 1916, published by 

 Mr. Abraham Flatters, 16-20, Church Road, Longsight, Man- 

 chester. I therefore need say nothing more on the subject. 

 Polyzoa require a larger cell for mounting than Rotifera, and 

 on this point I have some further remarks to make. After a 

 considerable search I found at Flatters & Garnett's some well-cut 

 glass cells (probably obtained from some makers in Germany), 

 cut and ground on both sides. These I treated in my own way 

 by painting on three successive coats of one of the caoutchouc- 

 gold-size cements, all within three days. I then dropped each of 



* Last year Professor Topsent of Dijon informed me that M. Raclais, 

 Professeur a V6co\e cle Pharmacie cle Paris, had lately prepared a cement 

 to close preparations mounted in water. Owing to the war I have been 

 unable to ask for or to obtain this cement. 



At an earlier date ]Mr. A. B. Aubert of New York City sent me a small 

 bottle of Micro-cement, which, however, I was unable to try at the time, 

 but as far as I can remember he mentioned that rubber was one of its 

 constituents. This year I wrote to him asking him for particulars 

 and details of its constitution. i\Iy letter, however, never reached him. 



I The firm is called Deutsche Spiogelglas Actien-Gesellschaft, in 

 Freden a/d Leine, Provinz Hanover, CJermany, English glass manu- 

 facturers might take the hint to produce white glass micro-slides of 

 equal f|uality and finish. 



