692 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for demonstration purposes. In an analogous manner may be preserved 

 macro- and microscopical preparations. For this purpose small glass 

 vessels like watch-glasses with flat bottoms are used. The floor is about 

 5 cm. in diameter, and the walls may ascend vertically or obliquely. 

 Upon these a thin glass cover is placed, after the nutrient medium, with 

 the bacteria to be cultivated, has been poured in. The organisms may 

 or may not be developed in an incubator. Low powers are always 

 available for inspecting the results of this method through the cover-glass, 

 and if the gelatin or agar layer be very thin higher powers can be used. 

 Before closing permanently it is advisable to wash the surface of the 

 gelatin, &c., with a sublimate solution 1 : 1000. Drops of moisture which 

 may condense on the cover and so obscure the colonies may be avoided by 

 placing on the top a piece of warm glass or metal. 



TJse of Styrax in Histology.* — Dr. P. Francotte recommends styrax 

 instead of balsam when the latter renders the object too transparent, e. g. 

 for bacteria and in the study of karyokinesis styrax gives a greater resolu- 

 tion than balsam, while its slightly yellow tint is eminently favourable for 

 photographic purposes. The author has obtained with ordinary plates ex- 

 cellent figures of the cells in the branchiae of larvae of salamander from 

 specimens mounted in styrax, while similar preparations mounted in 

 balsam required isochromatic plates or the use of chrysoidin previous to 

 the eosin. 



No excess of balsam necessary .f — Mr. J. E. Whitney emphasizes the 

 fact that there should not be any surplus balsam to remove from around 

 the cover. Experience soon learns to graduate the amount so that it will 

 fill the required space. The balsam slide and cover should be exactly 

 centered, and if the balsam happen to be too thick a very slight amount of 

 heat will make it flow to the edge. It is a good rule to mix a little less 

 balsam than seems necessary, as a little pressure will squeeze the balsam 

 right out to the edge. When a cell is used it is impossible, however, to 

 avoid some excess of balsam, as it needs to exude slightly around the cover 

 to drive out the air from the cell; but even in this case, if carefully 

 graduated to the cell, the excess need not be noticeable, and it can be 

 covered with a ring of cement without being cleaned away at all. 



Mounting Opaque Objects.:]: — Mr. C. M. Vorce deprecates the use of 

 pasteboard slides for mounting opaque objects ; for even when of heavy 

 tarboard they bend so readily as to crack or loosen the covers very easily, 

 and, unless well saturated with some resinous varnish, are liable to mould 

 or to take up moisture and deposit it under the cover. Even covered with 

 paper they do not stand reasonable wear. Wooden slips are vastly better, 

 and can be cheaply made by boring a hole centrally edgewise through a 

 piece of wood 1 in. thick and 3 in. long of any width, and slitting 

 it upon a saw table. But for this class of objects, for which low powers 

 will ordinarily be sufiicient, glass is the best material, and admits of 

 examining both sides of the object. For objects that must be viewed 

 uncovered and on both sides, no other mount will equal two of Pierce's 

 capped cells mounted back to back with the object between and fixed in a 

 wooden slip, either temporarily or permanently, or on a metal plate. 



Mounting Opaque Objects on a Micrometer Backgroiind.§ — Mr. E. 

 Parkes writes : — " Most people on looking at an object under the Microscope 



* Bull. Soc. Belg. Micr., xiii. (1887) pp. 144-6. 



t The Microscope, vii. (1887) r)p. 98-9. 



j Amer. Moii. Micr. Journ., viii. (1887) pp. 92-3. 



§ Trans, and Ann. Rep. Manchester Micr. Soc, 1886, pp. 58-9. 



