EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 51 



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

 warming slightly. 



{d) Wash in water. 



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



(/) Wash in water. 



(g) Dry. 



(h) Mount in Canada balsam. 



(According to Loffler, certain bacteria require the addition 

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

 many observers consider this unnecessary.) 



Another and very valuable method is that of Van Ermengeni. 



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

 ceding method. 



(b) 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 . . t part. 



Tannic acid, 10 to 25 per cent, solution 2 parts. 



(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 rein- 

 forcing bath:" 



Gallic acid. . . -5 grams. 



Tannic acid 3 grams. 



. Fused potassium acetate. lo grams. 



Distilled water 35° ^.c. 



(/) Ater a few seconds, replace the preparation in the nitrate 

 of silver solution, in which it is kept constantly moving, till the 

 solution begins to acquire a brown or black color. 



Some recommend leaving the preparation in the nitrate of 

 silver solution for two minutes in the first place, and in the 

 reducing bath for two minutes, without using the i^itrate of 

 silver solution a second time. 



