TU13ERCUL0SIS. 297 



fragment can be found, the purulent part is next best for 

 examination. 



In cases in which this ordinary procedure fails to reveal 

 bacilli whose presence is strongly indicated by the clin- 

 ical signs, the exact method of searching for them is to 

 partially digest the sputum with caustic potash, and then 

 collect the solid matter with a centrifugal apparatus. If 

 a very few bacilli are present in the sputum, this method 

 will often secure them. 



The material spread upon the cover-glasses should not 

 be too small in amount. Of course a massive, thick 

 layer will become opaque in staining, but should the 

 layer spread be, as is often advised, u as thin as possible," 

 there may be too few bacilli upon the glass to enable one 

 to make a satisfactory diagnosis. 



As usual, the material is allowed to dry thoroughly, 

 and is then passed three times through the flame for 

 purposes of fixation. 



EhrlicJC s Method, or the Koch-Ehrlich Method. — The 

 cover-glasses thus prepared are floated, smeared side 

 down, upon, or immersed, smeared side up, in, a small 

 dish of Ehrlich's anilin-water gentian-violet solution : 



Anilin, 4, 



Saturated alcoholic solution of gentian violet, 11, 

 Water, 100, 



and placed in an incubator or a paraffin oven, and kept 

 for twenty-four hours at about the temperature of the 

 body. When removed from the stain they are washed 

 momentarily in water, and then alternately in 25-33 

 per cent, nitric acid and 60 per cent, alcohol, until the 

 blue color of the gentian violet is almost entirely lost. 

 It must be remembered that the action of the strong acid 

 is a powerful one, and that too long a time must not be 

 allowed for its application. A total immersion of thirty 

 seconds is quite enough in most cases. After final thor- 

 ough washing in 60 per cent, alcohol the specimen is 



