120 CHAPTER X. 



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. 

 The 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 trans- 

 parent look that is easily recognisable. As soon as dry the 

 paraffin may be removed and they may be further treated 

 as desired. To remove the paraffin all that is requisite is 

 to put the slide into a tube of xylol or other good solvent, 

 which in a few seconds, or minutes at most, removes the 

 paraffin perfectly. Most workers first melt the paraffin, but 

 I find this is not necessary. 



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



perfectly, so that water will spread on it without any tendency 



to run into drops (see below). 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 lay it on a slab of 



thick glass, warmed, watching the flattening of the sections 



through a lens if necessary. As soon as they are perfectly 



flat, draw off the excess of water from one corner of the 



mount with a dry brush, and put aside to dry as before (a). 



In order to succeed in this method it is absolutely essential 



that the sections be perfectly expanded and come into close 



contact with the slide at all points. And to ensure this it 



is necessary that the slide should be perfectly free from 



grease, so that the water may wet it equally everywhere. 



The test for this is, firstly, to breathe on the slide ; the 



