94 PARAFFIN METHOD 



as we frequently prefer, simply plaster a wall of soft paraffin 

 (superheated) on to the upper and lower faces of the block with a 

 small spatula. Large blocks may have two coatings given them. 



It sometimes happens that the ribbon becomes electrified during the 

 cuttmg, and twists and curls about in the air in a most fantastic and 

 undesirable manner. It may be got flat by warming shghtly. Professor 

 leacher tells us that it is a great help to breathe on the razor as the 

 sections are coming off, the effect being to reduce electrification. 



175. Section Flattening. The sections having been obtained 

 may be cleared and mounted at once if they are quite perfect, 

 that IS, neither rolled nor creased nor compressed. But should 

 they in the least degree show any of these defects, they must first 

 be unrolled or smoothed, or expanded to their proper dimensions. 



The most efficacious plan is combined treatment with fluid 

 and heat. The sections are either floated on to the surface of 

 warm water or warm alcohol contained in a suitable dish, which 

 causes them to flatten out perfectly, and are then transferred 

 to a slide, by floating them into position, or otherwise. Or the 

 slide has a layer of water spread over it, the sections are laid on 

 the water, and the slide is heated (to somewhat below the melting- 

 point of the paraffin) until the sections flatten out, which happens 

 in a few seconds. 



A special water-bath for flattening sections is described by Nowak 

 in Zeit. iviss. Mik., xii, 1896, p. 447. 



« 



176. Clearing and Mounting. The sections having been duly 

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

 (Chapter XI), 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 creosote, creosote, a mixture of 

 turpentine and oil of cloves, benzol, 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 /x, it is ?iot 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. 



