144 



THE AMERICAN MONTHLY 



[August, 



for mounting, however, mostly come 

 from two sources, the Barbadoes and 

 the Nicobar Islands, where the fossils 

 occur in great abundance. 



To separate the perfect forms from 

 the mass of hard rock in which they 

 are found will be good work for one 

 evening at least, when the mounting 

 may be deferred to another time. 

 The rock is first disintegrated by boil- 

 ing in water containing some car- 

 bonate of soda, and the fine powder 

 is then boiled with dilute nitric 

 acid. After thorough washing the 

 powder is dried, and may then be 

 sifted through sieves of fine muslin, 

 or bolting cloth, which may be conven- 

 iently made by taking out the bottom 

 and top of a good-sized pill-box, and 

 stretching the cloth over it, forcing 

 the ring of the cover on to hold the 

 cloth. After sifting, the forms can be 

 picked out readily under a hand-lens, 

 or the sifted portions most rich in 

 good specimens, can be mounted as 

 they are. 



Polycystina may be mounted in sev- 

 eral ways, and however prepared they 

 make good slides for exhibition pur- 

 poses. If any readers are especially 

 desirous cf obtaining some of the Bar- 

 badoes material for cleaning, the 

 editor can supply a small quantity to 

 those who will send a stamped and 

 addressed envelope. 



Preparing Polycystina for 

 Mounting. — The ordinary appear- 

 ance of polycystina is clear and glassy. 

 They may be mounted in this condi- 

 tion, but for opaque objects they are 

 usually subjected to a strong heat for 

 a few seconds, which gives them a 

 beautiful porcellaneous appearance. 

 The best way of heating them is on 

 platinum foil. But as this is expensive 

 a;id not usually at hand, any conven- 

 ient means may be employed. A thin 

 s'rip of metal, or a piece of charcoal 

 may be used, the flame being directed 

 by means of a blow-pipe. 



Mounting in Balsam. — Either 

 the glassy or the heated specimens 

 may be used. In the early days of 



the New York Microscopical Society 

 we remember Mr. D. B. Scott used to 

 mount polycystina in balsam, to illus- 

 trate his method before the members, 

 and it is his method we will now de- 

 scribe. 



The forms are placed upon a slide, 

 with a consideralDle quantity of bal- 

 sam in benzole or chloroform, and the 

 cover-glass laid over them. The 

 babam is then heated until the ben- 

 zole or chloroform boils very briskly, 

 after which the slide cools, and the 

 work is done. The object of boiling 

 is to drive out air, and to distribute 

 the shells evenly. By using the dis- 

 solved balsam the slide can be finished 

 in a few minutes, for when the solvent 

 is driven off only hard balsam remains. 



Mounting Dry. — The finest slides 

 of polycystina are those prepared with 

 selected specimens, perfect in form 

 and arranged in groups. It is not 

 difficult or tedious to make a good 

 group of polycystina. It can be done 

 without any mechanical aid, although 

 many amateurs use mechanical fingers 

 of various degrees of complexity. Cer- 

 tainly there can be no more perfect 

 and beautiful slides of arranged ob- 

 jects than those mounted by Mr. 

 Arthur C. Cole, and they are all done, 

 even the finest groups of arrano^ed 

 diatoms, with the free hand. 



The cell for mounting may be pre- 

 pai^ed in any convenient way. In the 

 article by Mr. E. Ward all necessary 

 information about cells will be found. 

 A small, black, opaque central spot 

 can be put on with asphalt, upon 

 which the specimens maybe mounted. 

 This is better than to make the cell 

 entirely opaque, as it enables the 

 lieberkuhn to be used in illumination, 

 if desired. The specimens are fixed 

 in place by gum-arabic, a drop of a 

 weak solution being dried upon the 

 background, and moistened by breath- 

 ing upon it when the specimens are 

 placed in position. This causes ihem 

 to stick firmly, and when thoroughly 

 dry there is no danger of detaching 

 them by any ordinary handling. 



