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 wealher. Take the result for June 1, 

 1900 the air was 82 degrees Fa^irenheit, 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 

 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 effluent 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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