DISTRIBUTION OF B. COLI COMMUNE 
1 1 
showed B. coli to the number of 277 per c.c. The Manchester Ship Canal is not 
materially fouled by the addition of the Manchester sewage, containing, as it does, 
6,100 B. coli per c.c. before the sewage enters it, and 3,800 afterwards. 
B. NON-POLLUTED SUBSTANCES 
The same method of plating with carbolic agar has also been found convenient 
for the examination of substances that are not obviously polluted. In such cases a very 
low dilution, or none at all, has been employed, and the plates contain for the most 
part colonies that are not B. coli ; any colony that resembles B. coli, when looked at 
under the microscope, is investigated further by means of subcultures. As a rule, the 
distinction can be seen by merely observing the colony, and subcultures are made as a 
means of confirmation. The colony of B. coli is extremely typical on this medium, 
especially by its blue opalescence seen by transmitted light, and the oil-drop-like, 
colourless, appearance when viewed by reflected light. No colonies resemble those of 
B. coli exactly, though they may be a little like ; in these cases a subcultivation on 
agar and coverslip preparation will often settle the point. As will be seen in cases 
where there has been no obvious pollution no B. coli is found, and in these cases the 
plates are often found to be quite sterile. 
The substances examined were the following :— 
0) Air. 
(b) Snow. 
(<:) Rain and hail. 
(d) Dust. 
(<?) Virgin soil. 
(/) Streams and rivulets. 
(g) Sand of the sand filters of the Liverpool Waterworks. 
(b) Filtered and other drinking waters. 
(/) Grain and other food stuffs. 
(<?.) Air. — In the first experiments plates were poured and exposed to the air 
for 5, 15, 30 minutes. No B. coli were found, either in the air of the laboratory or in 
the air outside, by these means. 
To make a more complete search for the presence of the bacillus the following 
plan was adopted : — 
The air to be examined was drawn through a measured quantity of water in an 
Erlenmeyer flask, by means of a water pump, and measured by a gas meter. In the 
tube leading the air from the Erlenmeyer flask to the meter was a wool plug, and after 
the experiment was completed this plug was added to the water and well washed. 
Then 1 c.c. of this water was taken and plated. The air of the laboratory was 
analyzed in Experiments I and II. 
Experiment I. — 250 litres were drawn through in about 25 hours; three plates 
