142 CHAPTER X. 



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 success 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. It is not always 

 easy to obtain a slide that will fulfil these conditions. 



After slides have been cleaned by one of the processes 

 given in the Appendix, Cleaning Slides and Covers, they 

 should be rinsed with distilled water and preserved in 90 

 per cent, alcohol, from which they should be removed with 

 forceps when required for use not with the fingers then 

 simply drained, or wiped with a very clean cloth. If now a 

 slide will not stand the breath test, place a drop of water 

 on it and rub it in thoroughly with a damp cloth and try 

 again. 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 properly, it should 

 be rejected as incorrigible ; for there are apparently some 

 sorts of glass that can never be got to wet thoroughly. 



Tap water seems preferable to distilled water ; it seems to 

 spread better and give a stronger adhesion. NUSBAUM adds 

 a trace of gum arabic (one or two drops of mucilage to a 

 glass of water) ; and APATHY (Microtechnik, p. 126) adds 1 

 per cent, of Mayer's albumen (next ). 



Some workers have used alcohol (50 per cent, or 70 per 

 cent.) instead of water ; but this I believe to be now gener- 

 ally abandoned. 



This is the most elegant method of any. No cement 

 being employed, there is nothing on the slide except the 

 sections that can stain, or appear as dirt in the mount. 

 Tissues do not suffer in the least from the drying, provided 



