248 CHAPTER XIX. 



essential oils. But they have another useful property- 

 their low index of refraction. I find that that of euparal is 

 just right for most delicate cytological researches, giving 

 just the desired increase of visibility to unstained elements. 

 Thus I frequently find that unstained spindles which are 

 totally invisible in balsam become strongly visible in 

 the most minute details in euparal. The camsal balsam, 

 n = 1'478, I have also sometimes found valuable, but its 

 index is a little too low for most things, and I generally 

 prefer euparal, which I find I am now using almost as much 

 as balsam. I consider that all the media which have been 

 recommended on the score of a slightly lower index than 

 balsam, such as damar, colophonium, Venice turpentine, 

 castor-oil, are now superseded by these media. 



450. Sandarac (LAVDOWSKY, from Ref. Handbook Med. Sci., Supp. p. 

 438). Gum saiidarac 30 grs., absolute alcohol 50 c.c. Not trustworthy, 

 the mounts scale badly. 



451 . Photographic Negative Varnish (for mounting large sections 

 without cover- glasses) .See WEIGEBT, Zeit. wiss. Mik., iv, 1887, p. 209. 



452. Castor Oil. See GRENACHER, Abhandl. naturf. Ges. Halle-a.-S., 

 Bd. xvi; Zeit. iviss. Mik., 1885, p. 244. I have not had good results 

 with it. 



453. Terpinol. n = T484. See 131. 



454. Parolein (a pure form of paraffinum liquidum) is recom- 

 mended by COLES (Lancet, 1911, p. 878) as being quite neutral and 

 preserving certain coal tar stains. Ring mounts with Apathy's gum 

 syrup, 343. Its index is 1*471, which I find too low for most things. 



455. Cedar Oil. See 442, sub. fin. 



456. Gum Thus, dissolved in xylol, is recommended by EISEN, Zeit. 

 wiss. Mik., xiv, 1897, p. 201. 



457. Styrax and Liquidambar. See Journ. Hoy. Mic. Soc., 1883, p. 

 741 ; ib., 1884, pp. 318, 475, 655, and 827; and the places there quoted. 

 Also Bull. Soc. Beige de Mic., 188*, p. 178 ; and FOL, Lehrb., p. 141. 

 These are very highly refractive media, therefore seldom useful in 

 histology. 



