IOWA ACADEMY OF SCIENCES. 
259 
into account in considering the cause of these fluctuations. 
One is that during March and April there are greater fluct- 
uations in temperature, as well as in the humidity of the 
atmosphere and it is possible that such a condition might 
favor the rapid multiplication of bacteria. Again, in July 
and August and the major part of June, college was not in 
session, hence the sewage was not so strong. In a general 
way it would appear that the factors considered in connec- 
tion with the fluctuations of the effluent are applicable 
here also. 
One point which is rather interesting is that on different 
occasions, (June, July, 1900, also December of the same 
year), the average number of germs to the c.c. in the tank 
was larger than that of the manhole for the same period. 
The explanation of this seeming inconsistency seems sim- 
ple enough after taking into consideration the fact that 
bacteria increase very rapidly, and that the sewage is 
allowed to collect in the tank until 20,000 gallons have 
been accumulated, when it is discharged automatically by 
a Miller’s Automatic Siphon. Now, if the flow in the tank 
is slow (which is often the case) for any reason, the water 
stands longer, and hence more time is given the bacteria 
to multiply. 
It must be borne in mind that the environment in the 
tank is especially favorable for the rapid production of bac- 
teria as there is an abundance of organic matter present, 
while the tank being closed would tend to raise the tem- 
perature of the sewage rather than to lower it, which 
would further facilitate the rapid development of germ 
life. Leone’s experiments on the preserving of the Mang- 
fall water shows very clearly what might be expected from 
letting sewage accumulate slowly in the tank. It takes 
some times seventeen to twenty hours and even longer for 
the tank to fill. Below are given the tabulated results of 
his experiments together with some similar observations 
made by Cramer on the water from the Lake of Zurich. 
