54 LABORATORY BACTERIOLOGY 



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 io% solution of sulphuric 

 acid to the mordant. 



The flagella should appear as fine, hairlike appendages radi- 

 ating from the bacteria. 



83. 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 1 hour at room temperature, or 

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

 ration with distilled water, then .with absolute alcohol for 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 sil- 

 ver nitrate in distilled water. Allow the films to be in this for 

 from 2 to 3 minutes. Then without washing transfer to Solu- 

 tion C. 



Solution C (reducing and strengthening bath). 



Gallic acid 5 grams. 



Tannin 3 grams. 



Fused potassium acetate 10 grams. 



Distilled water 350 c.c. 



Keep in this for i to i|- minutes. Wash, dry, and mount. 

 It will also be found an advantage to use a fresh supply of Solu- 

 tion 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. 



