296 PATHOGENIC BACTERIA. 



Koch first stained the bacillus with an aqueous solu- 

 tion of a basic anilin dye to which some potassium 

 hydrate was added, subsequently washing with water 

 and counter-staining with vesuvin. Ehrlich subsequently 

 modified Koch's method, showing that pure anilin was 

 a better mordant than potassium hydrate, and that the 

 use of a strong mineral acid would remove the color 

 from everything but the tubercle bacillus. This modi- 

 fication of Koch's method given us by Ehrlich is at the 

 present time acknowledged to be the best method of 

 staining the bacillus. Many other methods have been 

 suggested, all of them, perhaps, more convenient than 

 Ehrlich's, but none so good. 



As being that most frequently performed by the 

 physician, we will first describe the method of seeking 

 the bacillus in sputum, for the purpose of making a diag- 

 nosis of the disease. 



If the material to be examined is sputum, and one 

 desires to be very exact in his examination, it is well to 

 have the patient cleanse the mouth thoroughly upon 

 waking in the morning, and after the first fit of coughing 

 expectorate into a clean wide-mouthed bottle. The object 

 of this is to avoid the presence of fragments of food in 

 the sputum. 



A better result will be secured if the examination is 

 made on the same day, because if the bacilli are few they 

 occur most plentifully in the small caseous flakes to be 

 described farther on, which are easily found at first, but 

 which break up and become part of a granular sediment 

 that always forms in decomposed sputum. 



The fresh sputum when held over a black surface 

 generally shows a number of grayish-yellow, irregular, 

 translucent granules somewhat smaller than the head of 

 a pin. These consist principally of the caseous material 

 from tuberculous tissue, and are the most valuable part 

 of the sputum for examination. One of the granules is 

 picked up with a pointed match-stick and spread over 

 the surface of a perfectly clean cover-glass. If no such 



