112 CHAr'J'ER IX. 



fr For oil of cajeput see § 129 ; and for this and other 

 clearers see also Jordan^ Zeit. wiss. Mik., xv, 1898, p. 51; 

 who recommends^ amongst other things^ oil of Linaloa^ which 

 remains colourless. 



The Newer Cdloidin Method. 



168. The New Method, by Clearing before Cutting.— This pro- 

 cess is due, I believe^ in the first instance to E. Meyee {Biol. 

 Oentralb., x, 1890, p. 508), who advised soaking blocks before 

 cutting for twenty-four hours in glycerin. Bumpus {Amer. 

 Anat., xxvi, 1892, p. 80) advises clearing the mass, after 

 hardening in chlorofoi-m, with white oil of thyme or other 

 suitable clearing agent (see § 167). The knife is wetted with 

 the clearing oil, and the same oil is employed for covering 

 the exposed surface of the object after each cut. Similar 

 recommendations are made by Byclkshymee {op. cit., pp. 351, 

 563), carbolic acid, or glycerin, or the mixture given § 167, 

 being suggested for clearing; and Gilson has for a long 

 time past adopted the practice of clearing before cutting 

 with cedar oil, as described in the next §. 



Fish {loc. cit., § 167) also advocates the practice of clear- 

 ing in the mass, recommending the clearing mixture there 

 given. Similarly Gage, Trans. Amer. Mile. Sue, xvii, 1896, 

 p. 361. 



All the authors above quoted cut in the wet way, that is 

 to say, with a knife wetted with the clearing liquid. 



169. Gilson's Rapid Process (communicated, April, 1892). 

 — The object is dehydrated, soaked in ether, and brought 

 into a test-tube with collodion or thin celloidin solution. 

 The tube is dipped into a bath of melted paraffin, and the 

 collodion allowed to boil (which it does at a very low 

 temperature) until it has become of a syrupy consistence. 

 (It should be boiled down to about one third of its volume.) 

 The mass is then turned out, mounted on a block of hardened 

 celloidin, and the whole hardened in chloroform or in a mixture 

 of chloroform and cedar oil for about an hour. It is then 

 cleared in cedar oil (if hardened in pure chloroform : special 

 clearing will not be necessary if it has been hardened in the 

 mixture). It may now be fixed in the microtome and cut. 



