92 APPLIED BACTERIOLOGY 



which the stain is washed off very thoroughly with water ; 

 the cover-glass is now air-dried and mounted in balsam. 



If the preparation is a successful one, the bacteria are of 

 a very dark-red colour, and much thicker than when stained 

 by the usual methods. In the ordinary processes of stain- 

 ing, only the protoplasmic body of the organism is coloured, 

 the outer sheath-like covering but rarely taking up any 

 dye at all; the above process, however, stains both the 

 cell-wall and the protoplasmic contents, thus making the 

 organism appear thicker than when stained in the ordinary 

 manner. The flagella should be seen as a number of very 

 fine curved threads, stretching out in an irregular manner 

 from the bacilli, more or less intensely stained. 



Van Ermengem's Method. — This method is easy, and gives 

 good results in careful hands. The following solutions are 

 prepared : 



(a) Osmic acid (2 per cent, solution), 1 part. 

 Tannin (10 to 25 per cent, solution), 2 parts. 



To each 100 c.c. of the tannin solution add 4 or 5 

 drops of acetic acid (glacial). 



(b) Nitrate of silver (-25 to "5 per cent, solution). 



(c) Gallic acid, 5 grammes. 

 Tannin, 3 grammes. 



Fused acetate of soda, 10 grammes. 

 Distilled water, 350 grammes. 



The cover-glasses, prepared and fixed as already directed 

 for Loffler's method, are covered with the osmic acid solu- 

 tion, which is allowed to act for half an hour. The cover- 

 glass is washed in a large excess of distilled water, and then 

 in alcohol. It is now dipped for three to five seconds in the 

 nitrate of silver solution (b), and then, without washing, 

 passed quickly through the gallo-tannic acid solution (c). 



The preparation is now washed again in a fresh quantity 

 of the silver nitrate solution (b), moving the cover-glass 



