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 cytologlcal researoheSj 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, oolophonium, Venice turpentine, 

 castor-oil, are now superseded by these media. 



450. Sandarac (Lavdowsky, from Bef. Haiidboolc Med. Sci,, Supp. p. 

 438). — Griim sandarac 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 Wbigebt, Zeit. wiss. Mile, iv, 1887. p. 209. 



452. Castor Oil.— See Gkenachee, Ahhandl. naturf. Oes. Halle-a.-S., 

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

 with it. 



453. Terpinol.— H = 1 ■484. See § 131. 



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

 mended by Coles {Lanset, 1911, p. 878) as being quite neutral and 

 preserving certain coal tar stains. Eing 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, suh.fin. 



456. Grum Thus, dissolved in xylol, is recommended by Eisen, Zeit. 

 wiss. Mile, xiv, l897, 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, 1881, p. 178 ; and FoL, Lekrh., p. 141. 

 These are very highly refractive media, therefore seldom useful in 

 histology. 



