306 SUMMARY OF CURRENT LIESEARCHES. 



Although by Methods 2 and 3 the platinum used is not recovered, 

 the weight of metal thrown away is extremely small and the cost is nol 

 great. The last two methods require further work to endeavour to gel 

 over the uncertainty and poor growth with the tetanus bacillus. 



Studying the Mitotic Spindle in the Spermatocytes of Forficula 

 auricularia.* C. F. V. Meek preserved the material obtained in July 

 and August, in Flemming's strong chromo-aceto-osmic acid fluid. The 

 testes remained in the fixative for twenty-four hours, and after washing 

 in running water and passing through upgraded alcohol, were cleaned in 

 xylol and embedded in paraffin. Sections were cut 8 //. thick with a 

 Cambridge rocking microtome. 



All sections were stained on the slide ; the slides were placed for 

 four to six hours in an aqueous solution of ferric alum, and were then 

 stained for twelve to fifteen hours in Heidenhain's iron-haematoxylin. 

 In certain cases they were first stained for ten minutes in eosin. The 

 preparations were studied with an apochromatic oil-immersion objective 

 of 2 mm. focus and X. A. 1 ■ 30 and compensating oculars. The light 

 was obtained from an inverted incandescent gas-burner, and was passed 

 through a Watson holoscopic oil-immersion substage condenser. The 

 photo-micrographs were made with a Zeiss camera, the apochromatic 

 objective mentioned above, and compensating ocular Xo. 4. The 

 camera extension was 50 cm. in the case of photographs of individual 

 cells, and 25 cm. in the case of photographs of cysts. The magnification 

 was estimated with a stage micrometer graduated to read one-hundredth 

 part of a millimetre. 



(2) Preparing- Objects- 



Crystal-grinding Apparatus.! — This instrument (fig. 32) was 

 designed by H. H. Thomas and W. C. Smith to facilitate "the cutting 

 and polishing of optically orientated parallel plates and prisms of 

 mineral substances. It consists of a triangular metal plate B, traversed 

 by three steel screws, one of which, S, carries a graduated head. The 

 pitch of the graduated screw is such that one revolution imparts a tilt 

 of half a degree to the axis of the instrument. This axis is occupied by 

 a solid metal cylinder P, capable of vertical movement and of rotation 

 within the graduated collar 1). After rotation it may be clamped in 

 any desired position by the screw C, but still retains its power to move 

 vertically. The lower end of the cylinder is drilled to receive a series 

 of chucks or crystal-holders which are bevelled off at angles different by 

 10° from each other, so that by the use of chucks and the graduated 

 screw S a face at any desired angle from ; to 90° may be cut and 

 polished upon a crystal. For the cutting of parallel plates and other 

 sections it is essential that the axis of the instrument should be first set 

 accurately normal to the grinding surface ; an optical method has been 

 found most suitable for this purpose, and the usual levelling system has 

 been dispensed with. A tube, carrying an optical flat F at its lower 

 end and a vertical illuminator E at its upper end, is inserted down the 



* Quart. Journ. Microscop. Sci. lxi. (1915), pp. 1-14 (2 pis.) 

 t J. Swift and Son's Catalogue (1914), pp. 26-7. 



