THE COLON GROUP OF BACILLI 139 



of anaerobic character giving large amounts of gas, 

 even up to loo per cent, a milky appearance and a 

 vile odor in lactose broth instead of the rather clean 

 acid smell characteristic of B. coli. 



Endo plates from these tubes were either atypical 

 or showed no growth. These organisms are probably of 

 the spore-forming B. sporogenes tyipe, a group which 

 we know from the work of Houston and others to be 

 widely distributed. Wells found this organism in the 

 water at Grand Forks, N. Dak., after treatment with 

 calcium hypochlorite. They appear to grow in decom- 

 posing organic matter, deposited sludge from sewage, 

 etc. The occurrence of this organism was noted by 

 A. J. McLaughlin in the report of the Commission to 

 investigate the waters of the International Boundary 

 (Rivers and Lakes Commission). 



The special significance of these facts is that when 

 some waters originally highly polluted reach the final 

 stages of purification these gas-forming anaerobes may 

 appear and make the presumptive test less delicate and 

 accurate. This seems to be especially the case in the 

 examination of waters in connection with the shell- 

 fish industry. 



This state of affairs is noted in the Potomac River 

 below Washington, as will be seen by the following 

 table kmdly furnished by Mr. W. F. Wells. (See page 



It is very evident from columns 2 and 5 that the 

 greater the number of B. coli the higher is the per- 

 centage efficiency of the presumptive test. 



A number of observers have also recently emphasized 



