METHODS OF EXAMINING MILK 275 
EXAMINATION FOR COLI 
The presumptive tests for Bacillus coli do not have 
the same value in milk examination as in water analysis, 
because it is practically impossible to obtain milk from 
the cow, even under good dairy conditions, without it 
being infected to some extent with colon bacilli from the 
intestines of the animal. The detection of this organism 
in milk is therefore of little value, except that when it is 
present in large numbers it is an evidence of uncleanli- 
ness and usually an indication of gross fecal contamina- 
tion. 
One of the presumptive tests for Bacillus coli in milk 
approved by the Laboratory Section of the American 
Public Health Association is made as follows: “1 c.c. of 
a 1 to 1,000 dilution of milk is placed in ordinary bile 
containing 1 per cent. lactose in a fermentation tube and 
allowed to stand at 87° C. for 72 hours, at the end of 
which time, if there is more than 15 per cent. gas, plates 
are made, colonies isolated and run through species tests.” 
The fermentation test described on page 278 is a 
simple and convenient method of detecting the presence 
of an excessive number of coli or other gas-forming or- 
ganisms in milk. 
EXAMINATION FOR TUBERCLE BACILLI 
The method recommended by the Laboratory Section 
of the American Public Health Association is as follows: 
“Pint or quart samples of milk should be obtained, 
kept well iced, and delivered to the laboratory as soon as 
possible. The milk and cream should be well mixed by 
shaking vigorously. 50 c.c. of the mixed milk are then 
transferred to a large centrifuge flask and 100 c.c. of 
sterile water added. Centrifuge for one hour at 2,000 
