WATER ANALYSIS. 1I9g 
be distinctly acid to indicate the presence of Bacil- 
lus coli. 
5. Isolation of Bacillus coli.—First Method.— 
(a) Add 50 c.c. of the water to be tested to 50 c.c. 
of sterile bouillon in a sterile flask. 
(6) Place in the incubator at 37.5° C. for two 
days. 
The high temperature will destroy the common 
water bacteria, but will encourage the growth of 
the coli group. 
(c) Test part of this culture for indol. Its pres- 
ence indicates the presence of Bacillus coli. 
(2) Make plates from this culture. 
(e) If any non-liquefying colonies are whitish 
with irregular leafy outlines and show lines more or 
less radial, they are probably colonies of Bacillus 
coli, and must be carefully studied in cultures.! 
Second Method.—(a) Add 70 c.c. of the water to 
be tested to 30 c.c. of sterile bouillon. 
(4) To the mixture add 1 c.c. of 5 per cent. car- 
bolic acid. 
(c) Incubate at 37.5° C. for twenty-four hours. 
Carbolic acid restrains the growth of the ordinary 
water bacteria, while the coli group and other 
intestinal forms grow unhindered. 
(7) From the growth that results inoculate fer- 
mentation-tubes containing 1 per cent. glucose 
bouillon. Note the amount of gas that forms as 
before. 
(e) Make plates from the growth in the tubes, 
1See page 60. 
