SERIAL SECTION MOUNTING 113 



tube of xylol or other good solvent, which in a few seconds, or 

 minutes at most, removes the parafTiii perfectly. Most workers 

 first melt the parafhn. but Lee found this is not necessary. 



{b) For series of numerous small sections. Clean a slide per- 

 fectly, 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 7iot to melt the 

 paraffin. Some persons do this by holding it over a small flame 

 for a few seconds. ' Lee preferred 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 moisture from the breath 

 should condense on it evenly all over, and disappear evenly. 

 Secondly, streaks of water drawn on it with a brush should not 

 run. To obtain a slide that will fulfil these conditions, clean it 

 well in the usual way, place a drop of water on it and rub it in 

 thoroughly with a damp cloth and try the tests. If this does not 

 suffice, take a turn of a corner of the cloth round a finger and 

 rub it with a piece of chalk, then damp the cloth and rub the 

 slide with it, finishing up with a clean part of the cloth and clean 

 water (De Groot, loc. cit., supra). If after performing this 

 operation twice the slide still refuses to take the water thoroughly 

 it should be rejected as incorrigible ; for there are apparently 

 some sorts of glass that can never be got to wet properly. Mayer 

 finds carbonate of magnesia or soda useful. 



GuDERNATSCH {Zeit. zviss. Mikr., xxiv, 1908, p. 358) washes 

 the slide well with potash soap, and arranges the sections on it 

 whilst still wet. Helly {ibid., 1906, p. 330) passes it two or 

 tliree times over the flame of a Bunsen burner. 



Tap water seems preferable to distilled water ; it seems to spread 

 better and to give a stronger adhesion. Nusbaum adds a traee of gum 



