THE MICROSCOPE AND MICROSCOPIC METHODS 53 



large drop of distilled water on a clean slfde, so that the water is 

 made very faintly cloudy. From the top of this drop one or 

 two transfers are made to a second drop with a small platinum 

 loop. From this second drop a loopful is transferred to a per- 

 fectly clean (flamed) cover-glass, spread with minimum manipu- 

 lation and dried quickly, high over the flame. 



(b) After drying, fixation is effected by passing through the 

 flame three times, holding the cover-slip between the thumb and 

 fore finger to avoid overheating. 



(c) The essential point in this method is the use of a mordant 

 as follows : 



Tannic acid, 10 per cent solution 20 c.c. 



Saturated solution of ferrous sulphate 4 c.c. 



Saturated alcoholic solution of fuchsin i c.c. 



This solution should be freshly prepared from pure substances, 

 and should be filtered at once after mixing. It may deteriorate 

 in a few hours but sometimes keeps for a few days or weeks. 

 A few drops are placed on the cover-glass, or the cover-glass is 

 placed, face down, in a dish containing the mordant; it is then 

 left for one to five minutes, the mordant being heated until it 

 steams. 



(d) Wash in water. 



(e) Stain with aniline-water fuchsin, or carbol-fuchsin, hot, 

 for one to two minutes. 



(/") Wash in water. 



ig) Dry. 



(h) Mount in Canada balsam. 



Another and very valuable method is that of Van Ermengem. 



(a) Make and fix cover-glass preparations as in the preceding 

 method. 



{b) Use the following mordant for one-half hour at room tem- 

 perature or for five minutes at 50° to 60° C. 



Osmic acid 2 per cent solution i , 



Tannic acid 10 to 25 per cent solution, 2 



(c) Wash carefully in distilled water and then in alcohol. 



