228 EXAMINATION AND PRESERVATION MEDIA. 



difficult cases you may pass through a mixture of the medium and 

 the solvent. 



These media work very kindly, and do not dry too rapidly. They 

 are not oxidant, and preserve delicate stains (perfectly, so far as I 

 know). The mounts seem to keep perfectly, without scaling : all 

 of mine, the oldest being eight years old, have kept without the 

 slightest deterioration in any respect. 



The primary intention of these media is to spare delicate objects 

 the usual treatment with absolute alcohol and 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 = 1478, 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 castor-oil, are now superseded by these media. 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, form Eef. Handbook Med. Sci., Supp., 

 p. 438). Gum sandarac 30 grs., absolute alcohol 50 c.c. Not trust- 

 worthy, the mounts scale badly. 



451. Photographic Negative Varnish (for mounting large sections 

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



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

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

 with it. 



453. Terpinol. n = 1-484. See 131. 



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

 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. Roy. Mic. Soc., 1883, 

 p. 741 ; ibid., 1884, pp. 318, 475, 655, and 827; and the places there 

 quoted. Also Bull. Soc. Beige de Mic., 1884, p. 178 ; and FOL, Lehrb., 

 p. 141. These are very highly refractive media, therefore seldom useful 

 in histology. 



