GUM AND GLYCERIN MEDIUM. 241 



This mixture never becomes turbid, and does not dry up. 

 The covers may be luted with asphalt or any other cement. 

 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 

 preparations of Hydroids, small Medusae, and other Coelen- 

 terates. 



393. Dean's Medium (see Micro. Diet, art. "Preservation"). Appears 

 to be now superfluous. 



394. Hoyer's Gum with Chloral Hydrate or Acetate of Potash 

 (Biol. Centralb., ii, 1882, pp. 23-4; Journ. 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. 



395. Gum and Glycerin Medium (F ARRANT' s medium; BEALE, 

 How to Work, &c., 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 1 grains; dissolve the arsenious acid in tlio 



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



incorporate with great care to avoid forming bubbles. 



Another method for making this medium is given by A. F. 

 STANLEY KENT in Journ. Roy. Mic. Soc., 1890, p. 820. 



396. Gum and Glycerin Medium (LANGERHANS' formula, 



16 



