ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 617 



suitable objects, and with stereo-photomicrography.' The booklet, which 

 forms one of a series (" Amateur Photographer's Library") should have 

 a ready vogue. 



(5) Microscopical Optics and Manipulation. 



Gullstrand, A. — Allgameine Theorie der monochromatischen Aberrationen and 

 ihre nachsten Ergebnisse fur die Ophthalmologic 



[Very fully discusses the general mathematical questions involved in passage 

 of light-rays through the eye, and deduces their special applications in 

 ophthalmology.] Nova Acta Reg. Soc. Sri. Upsalienni*, XX. 



fasc. 1 (1901) 204 pp. and .51 figs. 



(6) Miscellaneous. 



Zeiss' Crystal Films and Plates for Double Refraction.* — (i.) 

 Selenite and Mica Films. These are now supplied in four different 

 thicknesses which, when placed between crossed Nicol prisms, show red 

 of tho i., ii., iii., and iv. orders; there are also four different mica films, 

 which are graduated so as to produce differences of phase equal to 1 A, 

 i K ir K -k A< These eight films compose the set of selenite and mica 

 films originally proposed by H. v. Mohl for the examination of plant 

 cells in polarised light. 



(ii.) Bravais' Double Selenite Film. In this case two semicircular 

 films for red of the i. order are so arranged side by side that the equal 

 angles of optical elasticity are at right angles to each other, and form 

 angles of 45° to the boundary line. 



(iii.) Biot-Kleins Quartz Plate. This is a plate of quartz 3*75 mm. 

 thick, and cut perfectly perpendicularly to the axis. 



(iv.) Bertrand's Quadruple Quartz Plate. Four quadrant-shaped 

 quartz plates, cut perpendicularly to the axis, are cemented together so 

 that their dividing lines form the shape of a cross. Two of the plates 

 are composed of quartz with rotatory power directed to the right, the 

 other two of crystals having the opposite rotation. 



(v.) Stauroscopic Calc-spar Plate. This is a plate of calc-spar, cut 

 perpendicularly to the axis, mounted so as to be readily inserted between 

 eye-piece and analyser. 



B. Technique.! 

 CD Collecting: Objects, including- Culture Processes. 



Flask for Storing Culture Media-! — A. Eobin describes a simple 

 device for storing fluid culture media. It consists of a flask A plugged 

 with cotton-wool and sealed with a mixture of equal parts of paraffin and 

 vaselin, a bent tube d, and a siphon tube ab c (fig. 122). The end of the 

 tube d is loosely filled with cotton. The whole is sterilised, and then 

 the plug is pushed down the neck, leaving about one-half inch space from 

 the brim. The surface is dusted with powdered sulphate of copper, 

 and then the space in the neck above the stopper is filled in with a 



* Catalogue, English edition, 1902, pp. 104-5. 



t This subdivision contains (1) Collecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Imbedding and Microtomes ; 

 (4) Staining and Injecting ; (5) Mounting, including elides, preservative fluids, &c. ; 

 (6) Miscellaneous. 



% Journ. Applied Microscopy, v. (1902) pp. 1876-7 (1 fig.). 



