196 BARNETT COHEN 



deviating points. It is true that the error in the experimental method 

 employed is not inconsiderable and that a smooth curve might ade- 

 quately represent the course of events occurring but there is also a 

 danger of the eye being misled by an apparent regularity where none 

 may exist. 



The well-known higher resistance of Bad. coli is here again 

 exemplified. As will be seen further on, this resistance is of 

 utility in helping to throw light upon bacterial behavior during 

 the early stages of disinfection. 



Examination of figures 1 to 4 shows certain striking facts that 

 are common alike to both organisms in unbuffered surroundings. 

 The rate of decline in numbers does not always run parallel in 

 duplicate bottles held at the same temperature. This perplex- 

 ing result is consistently found in these four experiments and 

 inspection at once shows that the divergence is the result of a 

 chance distribution, some curves being generally parallel and 

 others far apart. Of course, this divergence if present increases 

 with the time elapsed, and depends upon the organism; for 

 Bad. ty-phosum being a matter of days, and for Bad. coli, one of 

 weeks. 



These results were further substantiated six months later, 

 when Bad. typhosum was studied in autoclaved tap water. This 

 experiment, no. 12, was carried out in triplicate, and every 

 precaution was taken to treat the samples alike. Yet in spite 

 of these efforts, the mortality in each of the triplicate bottles 

 followed a different course. (See table in Appendix.) 



What could account for the divergence of dupUcate bottles? 

 They were handled alike as nearly as possible, and the bottles 

 themselves, so far as we knew, were all of the same origin. The 

 dissolved gases could not be responsible, for, as will be seen later, 

 equilibrium with the air was attained within six hours from the 

 beginning of the experiment; and furthermore, in experiment 4 

 filtered tap water, which presumably retained all of its dissolved 

 gases, yielded the same result. 



A possible clue is furnished by the pH values of the water 

 determined at successive intervals. These values are noted 

 along the curves on the charts, and it becomes evident that du- 



