256 STEPHEN DEM. GAGE 



filters in which the free passage of the sewage is practically unre- 

 strained, while they are entirely absent from surface and ground 

 waters which have not been exposed to any considerable pollution. 

 It is rather surprising, however, that the numbers of bacteria of 

 this type in very polluted Merrimack River water were not larger. 



The information to be obtained by counts of bacteria and acid- 

 producing organisms at any one of the above temperatures is greatly 

 increased by the combination of the results obtained from counts 

 at two or more temperatures, and this information is much more 

 clearly shown if we express the relationship between the counts 

 at the different temperatures methematically. Many individual 

 differences between different waters are indicated by the bacterial 

 ratios which would not be apparent in the results of the counts. 



The writer is inclined to believe that a combination of counts 

 at 20 C. and at 40 C. with corresponding ratios will yield informa- 

 tion which will enable us to understand many of the hitherto unex- 

 plainable discrepancies in the results of bacterial analysis of water. 

 The combination of 20 and 30 counts appears to be of less value 

 while the value of 50 counts in combination with the other counts 

 has not been sufficiently studied to determine their applicability. 



In conclusion, the writer wishes to acknowledge his indebtedness 

 to the various members of the laboratory force at the Lawrence 

 Experiment Station for assistance in making the many determina- 

 tions, and to Mr. H. W. Clark, chemist in charge of the station, 

 whose hearty co-operation has made the investigation possible. 



REFERENCES. 



1. FULLER. Amer. Pub. Health Assoc. Rep., 1895, 20, p. 381. 



2. HESSE AND NIEDER. Ztschr. f. Hyg., 1898, 29, pp. 29, 454. 



3. WHIPPLE. Tech. Quarterly, 1902, 15, p. 127. 



4. G. HESSE. Ztschr. f. Hyg., 1903, 44, p. i. 



5. GAGE AND PHELPS. Amer. Pub. Health Assoc. Rep., 1901, 27, p. 392. 

 GAGE AND ADAMS. Jour. Infect Dis., 1904, i, p. 358. 



6. Report of Committee on Standard Methods of Water Analysis, Jour. Infect. 



Dis., Supplem., No. i, May, 1905. 



7. WURZ. Arch, de med. exp., 1892, 4, p. 85. 



8. MATTHEWS. Tech. Quarterly, 1893, 6, p. 241. 



9. WlNSLOW AND NlEBECKER. Ibid., 1903, l6, p. 227. 



10. GLOBIG. Ztschr. f. Hyg., 1888, 3, p. 294. 



