188 BAENETT COHEN 



To throw some light upon this controversy and at the same 

 time aid in an understanding of the mechanics of the disinfection 

 process, it seemed that a study based upon the following con- 

 siderations might prove useful. ]\Iost pre\'ious studies of disin- 

 fection were based upon results of the appUcation of an intense 

 disinfecting agent, like heat, heavy metals, acids, alkalis, etc. 

 As a result, the response of the organisms was prompt and the 

 period of their adjustment to the new conditions was so small 

 as to be overlooked. Only in exceptional cases, as the one cited 

 by Chick, where old cultures of Staphylococcus aureus were used, 

 was the early period long enough to excite attention; but in 

 that case the cultures used could not be considered as fairly 

 homogeneous. If the conditions causing death of the organism 

 could be toned down in intensity to a degree that might be termed 

 sub-lethal, then there should be an opportunity to observe their 

 adjustment from their manner of response. 



The reduction of lethal intensity may be satisfactorily accom- 

 plished by maintenance of the organisms at sufficientlj' low tem- 

 peratures on the one hand and by the control of the hydrogen 

 ion concentration of their environment on the other. 



EXPERIMENTAL 



The series of expermients reported and discussed below was 

 planned to give information on the following aspects of the 

 behavior of bacteria as represented by the colon-typhoid 

 organisms. 



1. The response of bacteria to the sub-lethal factors (in con- 

 tradistinction to disinfection as ordinarily understood) of starva- 

 tion and moderate intensities of hj^drogen ion concentration. 



2. The effect of moderate temperatures upon the rate of this 

 response. 



3. The analysis of the behavior in the Ught of the physico- 

 chemical concept of the disinfection process. 



A statistical method of approaching a solution of these ques- 

 tions appears at present to be the only satisfactory one; and 

 briefly stated, the method of study pursued was to expose Bad. 

 coli or Bad. typhosum to a given solution and follow periodically 



