IOWA ACADEMY OF SCIENCES. 
257 
example gives sufficient evidence of the possibility of the 
transmission of disease germs by means of water, and 
especially sewage. 
One question which presents itself on the accompany- 
ing data is the wide degree of fluctuation in the number 
of germs per c.c. found in the effluent. 
Take for example the results from June 1, 1900 to June 
15th, inclusive. The number of bacteria to the c.c. ranged 
from sixty on June 1st to 15,800 on June 15th. Why this 
difference? After considerable research and observation 
it seems that at least three factors would largely deter- 
mine the number of bacteria to the c.c. present at any par- 
ticular time. Perhaps of primary importance is the 
temperature of the sewage and thus indirectly of the soil 
through which it is filtered, and the air. It is a well rec- 
ognized fact that the warmer the sewage up to a certain 
point the faster the division of bacteria takes place, hence 
a larger number of germs would be found in warm sewage 
and during warm weather. Take the result for June 1, 
^ 1900 the air was 82 degrees Fahrenheit, the sewage 69 
degrees and the number of germs per c.c. is 60. The fol- 
lowing day, June 2nd, the air is one degree cooler and the 
water the same* temperature, yet there are 1,200 bacteria 
to the c.c. Take from the first of June to the 11th and 
although the temperature of the sewage is constant the 
number of germs per c.c. fluctuates from 60 to 15,800. The 
soil temperature for June 11th was 69 degrees. As the 
soil temperatures have been taken but once a week it is 
impossible to give its variations in temperature from day 
to day. 
Second, the condition of the sewage to be purified will 
A determine to a very great degree the number of bacteria 
to the c.c. but by comparison of the data it will be seen 
that this does not offer a satisfactory explanation in itself. 
Take for instance the results for November 14, 1899 as 
compared with those of June 19, 1900. While the num- 
ber of bacteria to the c.c. in the effluei.it varies only by 400 
. (November 14, 1899, 4,500. June 19, 1900, 4,100) the num- 
ber of germs in the raw sewage varies some five and one- 
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