236 COLLECTION, ETC., OF DIAT0MACEJ5. 



away. When, however, the finer varieties of Diatoms are required 

 as test objects, it is well to mount them directly upon the glass 

 cover. Geisbricht's method is as follows : — The slide is coated 

 with a solution of shellac in absolute alcohol, washing over this 

 with oil of cloves, and when the Diatoms are arranged in patterns, 

 warm the slide, and the oil of cloves is soon evaporated, leaving 

 only the work to be done of putting on the cover-glass, and the 

 filling in with either of the two mentioned media. Much has 

 been learnt of the internal structure of the valves of the Dia- 

 tomaceae by a series of experiments made by one of the most 

 prominent Belgian diatomists ; however, Mr. Sollas has furnished 

 us with his method, which is as practical as it can well be, and I 

 therefore append it as it appeared in a recent number of the 

 Journal of the Royal Microscopical Society : — 



*' My plan is to scrape off the green slime from our River mud 

 consisting chiefly of Pleiirosigma zigzag — a large species suitable 

 for cutting. The slime, together with some mud, unavoidably 

 gathered at the same time, is placed in a saucer and covered with 

 a piece of muslin which is to be in immediate contact with the mud, 

 while a film of water lies above it. The saucer is now exposed to 

 daylight, and the Diatoms creep through the muslin, collecting in 

 a consistent film on its upper surface. The muslin may now be 

 lifted from the mud, it comes away clean, bringing all the Diatoms 

 with it, but leaving the mud behind. The muslin with the 

 Diatom film is now immersed in the usual hardening and staining 

 re-agents. I have used a mixture of Chromic and Osmic Acid, and 

 absolute alcohol, for hardening ; borax-carmine, hsematoxylin, and 

 eosin for staining. When duly stained and hardened, the Diatom 

 film may be removed from the muslin without difficulty, and cut, 

 either by imbedding in pure paraffin and mounting in Canada 

 Balsam, or freezing in Gelatine jelly, which allows one to cut 

 consistent sections which f?iay be mounted direct in glycerine on a 

 glass slide, without passing through water." 



The knowledge which such a process imparts of the internal 

 structure of the Diatom is most important. 



