224 EXAMINATION AND PRESERVATION MEDIA. 



he adds 40 grins, of gelatin, dissolves with heat, and continues to 

 heat gently until the solution has somewhat thickened. This 

 remains fluid at ordinary temperatures. 



439. GILSON'S Chloral Hydrate Jelly (communicated by GILSON). 

 1 vol. of gelatin, melted secundum artem, and 1 vol. of Price's 

 glycerin. Mix, and add crystals of chloral hydrate until the volume 

 has increased by one-half ; warm till dissolved. This gives a very 

 highly refractive medium. 



GEOFFKOY, Journ. de Botan., 1893, p. 55 (see Zeit. wiss. Mik., ix, 

 1893, p. 476), dissolves, by the aid of as little heat as possible, 3 to 

 4 grms. of gelatin in 100 c.c. of 10 per cent, aqueous solution of 

 chloral hydrate. 



High Refractive Liquids. 



440. STEPHENSON'S Biniodide of Mercury and Iodide of Potassium 



(Journ. Roy. Mic. Soc. [N.S.], ii, 1882, p. 167). A solution prepared 

 by adding the two salts to water until each is in excess ; the liquid 

 will then be found to have a refractive index of 1-68. (If [AMANN, 

 Zeit. wiss. Mik., xiii, 1896, p. 21] glycerin be taken instead of water, 

 it rises to 1-78 or 1-80. BEHRENS [Tabellen, 1898, p. 71] takes 

 biniodide 65 parts, iodide 50, and water 25. n = 1-71.) Any 

 lower index can be obtained by suitable dilution with water. This 

 fluid is very dense, its specific gravity being 3-02. It is highly 

 antiseptic. 



For marine animals a weak solution is probably well adapted, as 

 about a 1 per cent, solution (5 minims to the ounce) will give the 

 specific gravity of sea water. 



Covers should be sealed with white wax, and the mounts finished 

 with two or three coatings of gold size and one of shellac. 



I have experimented both with strong and with weak solutions. 

 They are not adapted, I find, for the purposes of a permanent mount- 

 ing medium, for the preparations are- ruined by a precipitate which 

 forms in the fluid. But as a temporary examination medium I have 

 occasionally found this solution valuable. Its optical properties are 

 wonderful ; it allows of the examination of watery tissues, without 

 any dehydration, in a medium of refractive index surpassing that of 

 any known resinous medium. 



See further details in early editions. 



441. Monobromide of Naphthalin. See Journ. Boy. Mic. Soc., 1880, 

 p. 1043 (ABBE and VAN HEURCK), and Zool. Anz., 1882, p. 555 (MAX 

 FLESOH). 



