49 



Solution B. (sensitizing bath) This is a 5 per cent, solu- 

 tion 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 c.c. 



Keep in this for i to i}4 minutes. Wash, dry and mount. 

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

 C for each preparation, a small quantity being sufficient. 



EXERCISE XIX. 



STAINING TUBERCLE BACTERIA (BACILLI). 



§ 74. Explanatory note. The tubercle bacterium pos- 

 sesses the power of retaining when stained the coloring matter 

 when treated with a strong decolorizer such as a solution of 

 sulphuric or nitric acid. On this account its stain has a 

 high differential value which is made use of in identifying 

 this organism. Thus, in the examination of sputum in 

 cases of suspected tuberculosis, the object is to determine the 

 presence of tubercle bacteria. As this organism is not easily 

 cultivated the staining process is very largely depended upon 

 in making a diagnosis. 



§ 75. General Directions. Make three cover-glass 

 preparations from a culture of tubercle (furnished). Stain 

 these and carefully describe the appearance of the bacteria 

 and illustrate them with a few drawings. 



Stain a cover-glass preparation of tubercular sputum 

 (furnished). 



Read the directions in the text-books for staining tubercle 

 bacteria (bacilli). 



