SEWAGE CONTAMINATION OF OYSTER BEDS. 207 
BACTERIOLOGICAL ANALYSIS OF WATER SAMPLES FROM NARRAGANSETT 
BAY. 
Methods employed.—The usual methods for isolation of B. cold from 
water and sewage were used in this work. Fermentation tubes con- 
taining a neutral 1 per cent dextrose broth were inoculated with 1 ec. c. 
of the suspected water and incubated for three days at 837°C. In some 
cases a 0.1 per cent phenol broth was also inoculated with 1c. c. of the 
water and allowed to develop at 37° C. for twenty-four hours. Ina 
few tests litmus-lactose-agar and agar containing 1 per cent neutral 
red were sown with varying amounts of water and grown at incubator 
temperature. 
If no gas was formed in the fermentation tubes in twenty-four hours 
the test was considered negative without further procedure. If, how- 
ever, any considerable quantity of gas developed within this time, 
litmus-lactose-agar plates were inoculated in most cases from these 
tubes and incubated at 37° C. twenty-four hours longer. When litmus- 
agar plates were not used, a gelatin medium was substituted. Any red 
colonies developing on the litmus medium, and any colonies showing 
the characteristic growth of 2B. coli on gelatin, were fished out and 
transferred to slant agar tubes. From the cultures thus obtained 
subcultures were made in neutral dextrose and lactose broth, nitrate 
solution, milk, sugar-free broth containing 2 per cent of peptone 
and gelatin. When growth occurred in the phenol broth, although 
suflicient gas.to indicate the presence of 2. colz was not developed in 
the fermentation tubes,: litmus-lactose-agar plates were inoculated 
from the phenol broth and treated as already described. 
Organisms giving the following positive reactions to tests were 
regarded as members of the colon group of bacteria: 
1. A small more or less motile bacillus in twenty-four-hour bouillon 
or agar cultures. Usually not all the bacilli in one microscopic field 
are motile—often sluggishly motile. 
2. Fermenting dextrose broth with the production of gas. The large 
part, if not all, of the gas is formed during the first twenty-four hours. 
The liquid in the tube must be distinctly acid to indicate 2. coli. The 
ratio of hydrogen to carbon dioxide is approximately 2 to 1. This 
ratio is, however, more or less variable in cultures from a single 
strain. The total amount of gas produced in dextrose usually does not 
exceed 55 per cent, though there is also more or less variation in this 
characteristic. 
3. Fermenting lactose with the production of much gas; reaction 
strongly acid. 
4. Indol produced in sugar-free broth containing 2 per cent of 
peptone. 
5. Milk coagulated in three days at room temperature; in twenty- 
four hours at 87.5° C.; casein not liquefied; reaction acid. 
