66 LABORATORY BACTERIOLOGY 



for a few seconds in alcohol and again in water. It is then 

 ready for the microscopic examination in water, or it may be 

 allowed to dry and then be mounted in balsam. If the first 

 preparation fails, add 2 drops of a 10% solution of sulphuric 

 acid to the mordant. 



The flagella should appear as fine, hairlike appendages radi- 

 ating from the bacteria. 



97. Staining the flagella by Van Ermengem's method. The 

 films are prepared as described above. Three solutions are 

 necessary. 



SOLUTION A (FIXING BATH) 



Osmic acid, 2 % solution I part 



Tannin, 10-25 % solution 2 parts 



Place the films in this for i hour at room temperature or 

 heat in an oven for 5 to 15 minutes at 55 C. Wash the 

 preparation with distilled water, then with absolute alcohol for 

 from 3 to 4 minutes, and again very thoroughly in distilled 

 water. It is now ready to treat with Solution B. 



SOLUTION B (SENSITIZING BATH) 



This is a 5% solution of silver nitrate in distilled water. 

 Allow the films to be in this for from 2 to 3 minutes. Then 

 without washing transfer to Solution C. 



SOLUTION c (REDUCING AND STRENGTHENING BATH) 



Gallic acid 5 grams 



Tannin 3 grams 



Fused potassium acetate 10 grams 



Distilled water 350 cc. 



Keep in this for from i to i^ minutes. Wash, dry, and 

 mount. It will also be found an advantage to use a fresh supply 

 of Solution C for each preparation, a small quantity being 

 sufficient. If overbrowned, the background will be too deeply 

 stained ; if underbrowned, the flagella will be too faint. 



