GUM AND GLYCERIN MEDIUM. 201 



This mixture never becomes turbid and does not dry up. 

 The covers may be luted with asphalt or any other cementr 

 The fluid answers admirably for delicate Crustacea and their 

 larvae, the preparations do not shrink, and are not too much 

 cleared. It also answers well for hardened and stained pre- 

 parations of Hydroids, small Medusas, and other Coelenterates. 



377. Dean's Medium, see Micro. Diet., Art. " Preservation." Appears 

 to be now superfluous. 



378. Hover's Gum with Chloral Hydrate or Acetate of Potash 



(Biol. Centralh., ii, 1882, pp. 23-4; Jourti. Roy. Mic. Soc. 

 (N.S.), iii, 1883, pp. 144-5). A high 60 c.c. glass with a 

 wide neck is filled two thirds full with gum arabic (in pieces), 

 and then either a solution of chloral (of several per cent.) 

 containing 5 10 per cent, of glycerin, is added, or acetate of 

 potash or ammonia. The gum with frequent shaking dissolves 

 in a few days, and forms a syrupy fluid, which is slowly 

 filtered for twenty-four hours. The clear filtered fluid will 

 keep a long time, but if spores of fungi begin to develop a 

 little chloral can be added and the fluid refiltered. The 

 solution with chloral is for carmine or haematoxylin objects, 

 that with acetate for anilin objects. 



379. Gum and Glycerin Medium (FARRANT'S medium; BEALE, 

 How to Work, fyc., p. 58) : 



Picked gum arabic ... 4 ounces. 



Water 4 



Glycerin . . . . 2 



To be kept in a stoppered bottle with a lump of camphor. 

 This medium is quoted by Frey as consisting of equal 

 parts of gum, glycerin, and saturated aqueous solution of 

 arsenious acid. 



The Micrographic Dictionary gives the following directions : 

 Gum arabic 1 ounce, glycerin 1 ounce, water 1 ounce, 

 arsenious acid 1J grains; dissolve the arsenious acid in the ' 

 water, then the gum (without heat), add the glycerin, and 

 incorporate with great care to avoid forming bubbles. 



380. Gum and Glycerin Medium (LANGERHANS' formula, modi- 

 fication of FARRANT'S medium, Zool. Anzeig., ii, 1879, p. 575). 



Gummi arab. ..... 5*0 



Aquae 



