EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 59 



a dish containing the stain ; it is then left tor one to five min- 

 utes, warming slightly. 



(d) Wash in water. 



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

 (/) Wash in water. 



() Dry. 



(h) Mount in Canada balsam. 



(According to Loffler, certain bacteria require the addi- 

 tion 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 Er- 

 mengem. 



(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 I 



Tannic acid 10 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 re- 

 inforcing bath " : 



Gallic acid 5 grams. 



Tannic acid 3 grams. 



Fused potassium acetate 10 grams. 



Distilled water 350 c.c. 



(/) After 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 

 6 



