710 SUMMARY OP CURRENT RESEARCHES RELATING TO 



results. Its advantage consists in the fact that the ova do not become 

 porous, and that the segmentation spheres, as well as the nuclei, 

 remain fixed in their respective divisions. The ova may be cut like 

 cartilage. 



The composition of the fluid is : — 



Nitric acid (10 per cent.) 4 parts. 



Alcohol 3 „ 



Chromic acid (0 • 5 per cent.) .. .. 3 ,, 



which after a short time forms a violet fluid. 



In this the ova are placed for 4-5 hours, then for 24 hours in 

 70 per cent, alcohol, for a few days in strong alcohol, and for 4-5 

 days more in absolute alcohol. 



For staining, either (1) the fluid itself, or (2) the oil of cloves, can 

 be coloured. 



The first method is more convenient because quicker, since the 

 ova are hardened and coloured at the same time. The outer albu- 

 minous coat should, however, be removed, so that the staining fluid 

 may penetrate better. Some colouring agents, such as eosin, purpurin, 

 and aniline-violet, must be dissolved in three parts of alcohol before 

 they are added to the hardening fluid, whilst others, such as fuchsin 

 and aniline-red can be dissolved direct. Very beautiful pre- 

 parations are made by colouring the fluid with picrocarmine or borax- 

 carmine. 



To get rid of the sediment produced by these agents the fluid 

 must be filtered before the ova are laid in it. For washing, 5 per cent, 

 alcohol is first used (5 hours), then ordinary alcohol (10 hours), and 

 then absolute alcohol ; for clearing, oil of cloves ; and for mounting, 

 Canada balsam. 



By the second method the ova are hardened and cut, and the sec- 

 tion placed on the slide wetted with one or two drops of coloured oil 

 of cloves. In 5-10 minutes the latter is sucked away with filtering 

 paper. The oil can be coloured with eosin dissolved in alcohol or 

 with safranin. 



If entire ova or embryos are freed from their outer albuminous coat 

 and hardened, then taken out of the alcohol, left free until the alcohol 

 is evaporated, and then wetted with a few drops of oil of cloves or tur- 

 pentine, very excellent and stable preparations are obtained for the 

 study of the outer segmentation. 



Satterthwaite and Hunt's Freezing Section-cutter.* — Dr. T. E. 

 Satterthwaite, in conjunction with Dr. J. H. Hunt, has devised a 

 modification of the ordinary freezing microtome, shown in Fig. 134. 



It consists of the brass cylinder S, made of rather large size and 

 placed in the centre of a metallic box B. The length of the cylinder, 

 with milled head D, is about 5 inches. The diameter of the well a 

 is If inch. Fitted round the cylinder is a plate glass for the knife 

 to sweep over. 



* Satterthwaite, T. E., ' A Manual of Histology.' 478 pp. and 198 figs., 8vo, 

 London, 1881. 



