SERIAL SECTION MOUNTING. 341 



evaporated away from under the sections. This drying 

 may be performed at the temperature of the laboratory, in 

 which case many hours will be necessary (to be safe it will 

 generally be necessary to leave the sections overnight). 

 Or it may be performed in a stove or on a water-bath, at a 

 temperature a few degrees below the melting-point of the 

 paraffin (best not above 40 C.), in which case fixation will be 

 much more rapid, large thin sections being often sufficiently 

 fixed in an hour, though thick ones will require half a dozen 

 hours or more. T/ie paraffin must not be allowed to melt 

 before the sections are perfectly dry, the sections are sure to 

 become detached if it does. Perfectly dry sections have a 

 certain brilliant transparent look that is easily recognisable. 

 As soon as dry they are perfectly fixed, and the paraffin 

 may be removed and they may be treated with any desired 

 liquids without more risk of their falling off than is the case 

 with any other mode of fixation. To remove the paraffin 

 most workers first melt it, and then remove it with a solvent. 

 I find this is' by no means necessary, all that is requisite is 

 to put the slide into a tube of xylol, which in a few seconds, 

 or minutes at most, removes the paraffin perfectly without 

 any heat. 



(b) For series of numerous small sections. Clean a slide 

 perfectly, so that water will spread on it without any ten- 

 dency to run into drops (see p. 142). Breathe on it, and 

 with a brush draw on it a streak of water as wide as the 

 sections and a little longer than the first row of sections 

 that it is intended to mount. With a dry brush arrange 

 the first row of sections (which may be either loose ones or 

 a length of a ribbon) on this streak. Breathe on the slide 

 again, draw on it another streak of water under the first one 

 and arrange the next row of sections on it, and so on until 

 the slide is full. Then breathe on the slide again, and with 

 the brush add a drop of water at each end of each row of 

 sections, so as to enable them to expand freely ; then warm 

 the slide so as to flatten out the sections, taking care not to 

 melt the paraffin. Some persons do this by holding it over 

 a small flame for a few seconds. I prefer to keep a slab of 

 thickish glass in the drawer of the water-bath, so as to have 

 it warm, and lay the slide on it, watching the flattening of 

 the sections through a lens if necessary. As soon as they 



