CHAPTER IX. 103 



or Dunham's mixture of 3 or 4 parts of white oil of thyme with 

 1 part of oil of cloves. (As to oil of thyme, see also 125, 126.) 



FISH (Proc. Amer. Mik. Soc., 1893) advises a mixture of 1 part of 

 red oil of thyme with 3 parts of castor oil, the latter being added 

 in order to counteract the volatility of the thyme oil. But later 

 (June, 1895), writing to me, Dr. Fish says he has substituted the 

 white oil of thyme for the red, and finds it an advantage in orien- 

 tating. See also 126, and under " Euparal." 



Some specimens of clove oil dissolve collodion very slowly, and may 

 be used, but I would not be understood to recommend it. The action 

 of origanum oil varies much, according to the samples ; some sorts do 

 not clear the collodion, others dissolve it, others pucker it. MINOT 

 (Zeit. wiss. Mik., iii, 1886, p. 175) says that Dunham's mixture " clarifies 

 the sections very readily, and softens the celloidin just enough to prevent 

 the puckering which is so annoying with thyme alone." 



Carbolic acid has been recommended. WEIGERT (Zeit. wiss. Mik., iii, 

 1886, p. 480) finds that a mixture of 3 parts of xylol with 1 part of 

 carbolic acid (anhydrous) clears well. But it must not be used with the 

 basic anilin stains, as it discolours them. For these anilin oil may be 

 used with xylol in the place of carbolic acid. 



Anilin oil clears well (it will clear from 70 per cent, alcohol), but 

 unless thoroughly removed the preparation becomes yellowish-brown, 

 see 134. See VAN GIESON, Amer. Mon. Mic. Journ., 1887, p. 49, or 

 Journ. Roy. Mic. Soc., 1887, p. 519, for a review of these clearing agents. 



Beech-wood creasote has been recommended (by M. Flesch). 



EYCLESHYMER (Amer. Nat., xxvi, 1892, p. 354) advises a mixture of 

 equal parts of bergamot oil, cedar oil, and carbolic acid. 



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 Celloidin Method. 



168. The New Method, by Clearing before Cutting. This process 

 is due, I believe, in the first instance to E. MEYER (Biol. Centralb., 

 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 chloroform, 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 EYCLESHYMER (op. cit., 

 pp. 354, 563), carbolic acid, or glycerin, or the mixture given 167, 

 being suggested for clearing ; and GILSON has for a loner time past 



