EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 47 



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

 flame three times. 



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



as follows: 



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



Saturated solution of ferrous sulphate 5 c.c. 



Saturated alcoholic solution of fuchsin i c.c. 



This solution is filtered and a few drops are placed on the 

 cover-glass, or the cover-glass is placed, face down, in a dish 

 containing the stain; it is then left for One to five minutes, 

 warming slightly. 



{d) Wash in water. 



(e) Stain with anihne-water fuchsin, or carbol-fuchsin. 



(/) Wash in water. 



{g) Dry. 



Qi) Mount in Canada balsam. 



(According to LofHer, certain bacteria require the addition 

 of an acid solution, and certain others an alkahne solution, but 

 many observers consider this unnecessary.) 



Another and very valuable method is that of Van Ermengem. 



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

 method. 



(6) Use the following mordant for one-half hour at room- 

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



Osmic acid, 2 per cent, solution j i 



Tannic acid, lo to 25 per cent, solution 2 



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



{d) Place for a few seconds in a 0.25 to 0.50 per cent, solution 

 of nitrate of silver — "the sensitizing bath." 



(e) Without washing transfer to the "reducing and reinforcing 

 bath": 



Galhc acid 5 grams. 



Tannic acid 3 grams. 



Fused potassium acetate 10 grams. 



Distilled water 350 c.c. 



