252 



Stephen DeM. Gage 



decreasing in proportion as the amount of oxygen in the water in- 

 creased. 



The seasonal distribution of B. coli in samples of Merrimack 

 River water has been discussed in a former pubhcation'^ in which 

 it was shown that the average numbers of B. coli were higher during 

 the summer months than during the winter months. A similar 

 variation can be noted in Table i8, in which the bacteria and B. 

 coli and the ratio between the two have been arranged according 

 to the temperature of the water at the time the samples were col- 

 lected. The maximum numbers of both bacteria and B. coli occurred 

 in samples from both locations when the temperature of the water 

 was between 60° and 70° F., and the minimum numbers of bacteria 

 were found when the temperature was between 40° and 50° F. The 

 temperatures at which the minimum numbers of B. coli were found 

 in samples from the two locations do not agree, being lowest in the 

 canal water when the temperature was between 40° and 50° F., and 

 lowest in the Intake samples when the temperature was between 

 30° and 40° F. The bacteria-jB. coli ratios were highest when the 

 temperature was highest and lowest when the temperature was 

 lowest, the values for intermediate temperatures, however, appearing 

 to follow no definite curve. 



TABLE 18. 

 Relation between Temperature and Bacterial Contents of Merrimack River Water. 



The averages of bacterial determinations and the bacteria-.B. 

 coli ratios, arranged according to the volume of water flowing in 

 the river, are shown in Table 19. Both bacteria and B. coli decreased 

 as the volume of the river increased. We should expect this to be 

 the case in a river such as the Merrimack, in which a large proportion 

 of bacteria and B. coli are contributed by the sewage entering that 

 river, the effect of dilution overbalancing other factors, such as wash- 



