92 BACTERIOLOGY. 



bacillus is only slightly infectious for cattle, but the 

 bovine bacillus is infectious for human beings, par- 

 ticularly young children, who may become infected 

 from the milk of tuberculous cattle. 



staining The tubercle bacillus does not stain readily, but 



once stained it is difficult to decolorize it with acids. 

 For this reason it is said to be acid-fast. The method 

 employed in staining is as follows: The suspected 

 material is spread thinly on a glass slide and dried. 

 The preparation is then covered with fuchsin, a red 

 dye to which has been added a small amount of car- 

 bolic acid solution and steamed, the heat quickening 

 the staining. Then the preparation is washed off in 

 water and decolorized with a 5 per cent, solution of 

 nitric acid. This is allowed to act until all the red 

 color is removed. After washing again in water the 

 preparation is again stained with a methylene-blue 

 solution. The picture produced by this method shows 

 the tubercle bacilli unaffected by the acid decolorizer 

 and stained red, while all other organisms are stained 

 blue. In this way the tubercle bacillus may be de- 

 tected in discharges from suspected cases. 



Tubercle In collecting urine for examination for tubercle 



bacilli in t M 



urine bacilli it is important to know that the smegma bacil- 

 lus, a non-pathogenic organism found in the secre- 

 tions about the genitalia, possess the same staining 

 peculiarities as the tubercle bacillus ; so that great care 

 must be used to exclude it from the urine by careful 

 cleansing of the external genitalia and collection of 

 the urine by catheter. In fluids like urine, pleural effu- 



