96 
BACTERIOLOGY. 
Staining 
Tubercle 
bacilli in 
urine 
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. 
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 fuehsin, 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. 
In collecting urine for examination for tubercle 
bacilli it is important to know that the smegma bacil¬ 
lus, a n on-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- 
