172 PATHOGENIC BACTERIA. 



These peculiarities delayed the discovery of the bacil- 

 lus for a considerable time, but now that we are familiar 

 with them they give us a most valuable diagnostic cha- 

 racter, for with the exception of the bacillus of lepra no 

 known bacillus reacts in exactly the same way. 



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. 



If one desires to be very exact in his examination, 

 it may be 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. 



The physician will secure a better result if the exam- 

 ination be made on the same day than if he wait a num- 

 ber of days, because if the bacilli are few they occur 

 most plentifully in the small caseous flakes to be de- 

 scribed 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 



