228 EXAMINATION AND PRESERVATION MEDIA 



The primary intention of these media is to spare dehcate objects the 

 usual treatment with absolute alcohol and essential oils. But they 

 have another useful property — their loiv index of refraction. We find 

 that that of euparal is just right for most delicate cytological researches, 

 giving just the desired increase of visibility to unstained elements. 

 Thus we 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, Lee has sometimes found 

 valuable, but its index is a little too low for most things, and he generally 

 used euparal. We consider that all the media which have been recom- 

 mended on the score of a slightly lower index than balsam, such as 

 damar, colophonium, Venice turpentine, castor-oil, are now superseded 

 by these media, 



490. Denham's Sandarac Camphloral {Journ. Roy. Mic. Soc, 

 1923). Two parts by w^eight of crystalline chloral hydrate are 

 ground in a glass mortar with one part of " flowers of camphor." 

 If any difficulty is found in getting the last few crystals to dis- 

 solve the mixture is left in a warm place for a few hours. The 

 liquid is then filtered. The sandarac solution is prepared 

 separately. Selected crystals of the gum are dissolved in excess 

 of isobutyl alcohol at 60° C. to make a solution thin enough to 

 filter easily. It is then shaken up with animal charcoal, and 

 filtered several times through paper, after which it is evaporated 

 to a thick syrup, using a condenser to receive the alcohol. One 

 part of gum is mixed with two of camphloral, and incorporated 

 by warming and stirring. The product should have a refractive 

 index of 1-485. Objects may be mounted from 70 per cent, 

 alcohol. Euparal is commercially made in much the same way, 

 the gum being dissolved in eucalyptol. 



491. Sandarac (Lavdowsky, from Ref. Handbook Med. Sci., Supp., 

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

 worthy, the mounts scale badly. 



492. Photographic Negative Varnish (for mounting large sections 

 without cover-glasses). See Weigert, Zeit. iviss. Mik., iv, 1887, 

 p. 209. 



493. Castor Oil. See Grenacher, Ahhandl. naturf. Ges. Halle-a.-S., 

 Bd. xvi ; Zeit. zviss. Mik., 1885, p. 244. Lee did not have good results 

 with it. 



494. Terpinol. n = 1484. See § 147. 



495. 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 Api'ithy's gum syrup, § 511. 

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



496. Cedar Oil. See § 482, siib fin. 



497. Gum Thus, dissolved in xylol, is recommended by Eisen, Zeit. 

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



498. 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 Btill. Soc. Beige de Mic, 1884, p. 178 ; and Fol, Lehrb., 

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

 in histology. 



