CHAPTER VIII. 91 



150. Clearing and Mounting.- The sections having been duly 

 smoothed by one of these processes, and duly fixed to the slide 

 (Chapter X), unless it is desired to keep them loose, all that now 

 remains is to get rid of the paraffin and mount or stain as the case 

 may be. Many solvents have been recommended for this purpose : 

 Turpentine, warm turpentine, a mixture of 4 parts of essence of 

 turpentine with 1 of creasote, creasote, a mixture of turpentine and 

 oil of cloves, benzin, toluol, xylol, thin solution of Canada balsam 

 in xylol (only applicable to very thin sections), hot absolute alcohol, 

 naphtha, or any other paraffin oil of low boiling-point. Of these 

 xylol and toluol are generally in most respects the best. Benzol and 

 chloroform are too volatile for safe manipulation. 



If the slide be warmed to the melting-point of the paraffin, a few 

 seconds will suffice to remove the paraffin if the slide be plunged into 

 a tube of xylol or toluol. For thin sections, 10 to 15 jut, it is //.// 

 necessary to warm at all. The sections may be mounted direct from 

 the xylol, or the slide may be brought into a tube of alcohol to remove 

 the solvent for staining. 



Paraffin sections can be stained without removal of the paraffin, so 

 that after-treatment with alcohol can be suppressed, but this is only 

 very exceptionally advantageous. 



151. Pure Paraffin. It is now almost universally admitted that 

 pure paraffin is superior for ordinary work to any of the many 

 mixtures with wax and the like that used to be recommended. 

 Paraffin varies enormously in hardness according to the temperature 

 of its surroundings. It should therefore be taken of a melting- 

 point suitable to the temperature of the laboratory. A paraffin 

 melting at 50 C. or a little harder, is that which in my expern-m 

 gives the best results so long as the temperature of the laboratory is 

 between 15 and 17 C. For higher temperatures a harder paraffin 

 is required, and for lower temperatures a softer one. 



Many workers of undoubted competence prefer masses somewhat 

 harder than this ; so, for instance, Heidenhain (58), Apathy J55), 

 Rabl (56), Mayer (58 to 60 in summer ; in winter about 56, but 

 never less than 50). Mayer points out that at Naples the tempera- 

 ture during five months of the summer and autumn is over 22 C 

 the laboratory, sometimes over 30. Temperatures such as these are 

 seldom realised in the British Isles, and, whilst I quite admit that 

 such hard paraffin may have its raison d'etre for Naples, I hold that i 

 that very reason it is in general unnecessarily hard for cooler climai 



My recommendation of a relatively soft paraffin refers to wor 

 with the Thoma sliding microtome. Microtomes with fixed knives, 



