MICROSCOPIC EXAMINATION 135 



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 

 preparation with distilled water, then with absolute alcohol 

 for from 3 to 4 minutes, and again very thoroughly in disr- 

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



SOLUTION B (SENSITIZING BATH) 



This is another 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 1 to 11/2 minutes. Wash, dry, and 

 mount. It is 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. 



. The use of mordants and decolorizing agents. In films 

 of blood and pus, and in tissue sections, the tissue elements, 

 may be stained to such an extent as to obscure the bacteria. 

 Hence many methods have been devised to use substances 

 which, while increasing the staining power, tend to fix the 



stain in the bacteria and further to treat the preparations with 

 substances which decolorize the overstained tissue to a greater 



.or less extent, while leaving the bacteria stained. The stain- 

 ing capacity of a solution may be increased by (a) the addi- 

 tion of substances such as carbolic acid, aniline oil, or metallic 

 salts, all of which probably act as mordants; (b) by the ad- 

 dition of weak alkaline solution, especially of caustic potash 

 or ammonium carbonate; (c) by the employment of heat; (d) 

 by long duration of the staining process. 



Staining acid fast bacteria. The tubercle bacterium is. 



