45 
The change between the two extremes is of course a very 
violent one, but it is easily demonstrated that in nature the 
process isa gradual one. Inorder further to investigate the 
change described above, three separate investigations were 
undertaken :— 
I. Situated in the compound of the laboratory is a large 
tank about an acre and a half in extent. This, during the hot 
weather months, usually contains quite a good water, that is 
to say, a surface sample contains no lactose fermenters in 
5 c.c. Generally, however, the glucose + lactose — are rather 
numerous. Into this large pond was thrown two or three 
tubs full of nightsoil, cowdung, effluent, etc., care being taken 
to distribute the material over the water and to make a mix- 
ture. Analyses were made on succeeding days after it had 
been polluted in this way. Four separate investigations of 
this nature were carried out and the results are almost identical 
in every case. Several other points were also investigated 
during these experiments. Table No. VI(e) gives the details 
of experiment, samples being taken both from the surface and 
from the bottom of the tank. 
Before discussing the results it is necessary to point out 
certain obvious objections to these experiments. First, we 
did not begin with sterile water, and therefore it is impossible 
really to be quite sure that the organisms which remain to the 
end of the experiment were not those originally present in 
the tank. Secondly, the gap between ‘1 and -or in our esti- 
mation is too wide to show delicate shades of difference between 
the acid and gas line in both media. Thirdly, the feces used 
were obtained in the hot weather when very few varieties of 
organisms are normally present. The bacilli isolated at this 
time have a tendency to belong to the resistant varieties. 
Making due allowance for these objections the following 
points are demonstrated by the table :— 
(1) That on all occasions when the water has been 
recently polluted, acid and gas line in the glucose and lactose 
medium is the same in both cases. 
(2) Within a very few days there is a very rapid decrease 
in all the fecal organisms irrespective of class. 
