224 EXAMINATION AND PRESERVATION MEDIA 



been incorporated about 50 c.c. of fresh egg-albumen ; mix 

 thoroughly, and heat to boiling-point for about five minutes. 

 Make up the total weight to 1550 c.c. with chloroform water. 

 Filter in a warm chamber. 



477. Heidenhain {Zeit. iviss. Mik., xx, 1905, p. 328) takes of 

 gelatin 9 parts, glycerin 7, and water 42, and to the filtrate adds 

 drop by drop 14 j^arts of absolute alcohol. 



478. Fischer {Zeit. wiss. Mik., xxix, 1912, p. 65) takes 5 grm. of 

 borax dissolved in 240 c.c. of water and adds 25 c.c. of glycerin. 

 To this he adds 40 grm. of gelatin, dissolves with heat, and con- 

 tinues to heat gently until the solution has somewhat thickened. 

 This remains fluid at ordinary temperatures. 



479. Gilson's Chloral Hydrate Jelly (communicated by Gilson). 

 One 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. 



Geoffroy, 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 grm. of gelatin in 100 c.c. of 10 per cent, aqueous solution 

 of chloral hydrate. 



HIGH REFRACTIVE LIQUIDS 



480. Stephenson's Biniodide of Mercury and Iodide of Potassium 

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

 Mik., xiii, 1896, p. 21] glycerin be taken instead of water, it rises to 

 1-78 or 1-80. Behrens [Tnbellen, 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. 



Lee has experimented both with strong and with weak solutions. 

 They are not adapted for the purposes of a jiermanent mounting medium, 

 for the preparations are ruined by a precipitate which forms in the fluid. 

 But as a temporary examination medium Lee occasionally found this 

 solution valuable. Its optical properties are wonderful ; it allows of 

 the examination of watery tissues, ivithout any dehydration, in a mediiun 

 of refractive index surpassing that of any known resinous medium. 



See further details in earty editions. 



481. Monobromide of Naphthalin. See Journ. Roy. Mic. Soc., 1880, 

 p. 1043 (Abbe and Van Heurck), and Zool. Anz., 1882, p. 555 (Max 

 Flesch). 



RESINOUS MEDIA 



482. Resins and Balsams. Resins and balsams consist of a 

 vitreous or amorphous substance held in solution by an essential 



