IOWA ACADEMY OF SCIENCES. 
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making parallel cultures the relative number of gas pro- 
ducers present in a c.c. of sewage. 
A method which has given excellent results is as fol- 
lows: Take a tube of ordinary agar, melt and pour in a 
petri dish, after it has cooled to such a degree that it is 
just liquid, add one-tenth cc. of sewage and immediately 
turn it around rapidly in order to secure equal distribu- 
tion of the sewage; then, after it has been cooled so far as 
to become solid, add another tube of melted agar, care 
being taken that it is not too hot, after which, without 
stirring, set it away to develop. This last agar forms a 
layer containing no germs, if the work has been properly 
done. The anaerobic gas producers working in the lower 
portion produce gas, which appears in the agar as minute 
air bubbles. 
The effluent of July 12, 1900, after standing one week, 
showed 25 gas producers in the plate, and as one-tenth 
c.c. of sewage from the effluent was used in making the 
culture, there would be 250 gas producers to the c.c. of 
effluent. The number of germs counted from a parallel 
culture was 2,400, which means that approximately ten 
per cent of the total number of germs were gas producers, 
the above result being obtained from the sample of efflu- 
ent taken from the west bed. The temperature of the air 
and sewage being 72° Fahrenheit. A similar culture from 
the tank on the same date showed 1 IB gas producers in the 
plate, making 114, 130 gas producers to the c.c. of sewage, 
or about 33^ per cent of the germs in the tank at that time 
were gas producers, the temperature of the sewage in the 
tank being 62°. The total number of germs for the c.c. 
being 342,400. 
The manhole sample taken July 12th and examined July 
17th, shows a still greater percentage, there being 104,030 
gas producers to the c.c., or 43 per cent of the germs in the 
raw sewage at that time were gas producers. The tem- 
perature of the raw sewage was 68°, the total number of 
germs to the c.c. on an ager culture being 242,400. Other 
cultures were made in the same manner, with approxi- 
mately the same results. 
