DISINFECTION STUDIES' 



THE EFFECTS OF TEMPERATURE AND HYDROGEN ION CON- 

 CENTRATION UPON THE VIABILITY OF BACT. CO LI 

 AND BACT. TYPHOSUM IN WATER 



BARNETT COHEN 



Division of Chemistry, Hygienic Laboratory, United States Public Health Service, 



Washington, D. C. 



Received for publication May 21, 1921 



Exposure to extremes of temperature and of hydrogen ion 

 concentration produces an accelerated death rate of bacteria. 

 These are typical conditions of ordinary disinfecting procedures. 

 Temperatures and hydrogen ion concentrations in the zones 

 between those which are favorable and those which are distinctly 

 lethal may be expected to produce an adaptation in the organisms 

 or a comparatively slow death rate, knowledge of which may 

 reveal the conduct of bacteria under moderately unfavorable 

 conditions in nature, and add to our understanding of certain 

 phases of disinfection. 



The object of this study was to investigate the effects of varia- 

 tions in moderate temperature and moderate hydrogen ion con- 

 centrations upon the death rate in water and dilute buffer solu- 

 tions. The experimental method imposed sub-lethal conditions 

 upon the bacteria in contradistinction to the accelerated death 

 induced by ordinary disinfecting procedures. 



It has been found in unbuffered media like distilled water or 

 tap water that the death rates vary coincidently with apparently 

 unimportant shifts in hydrogen ion concentration. When the 

 pH factor is controlled by means of M/500 buffers, the death 

 rates are stabilized so that comparisons become possible. The 



' Published by permission of the Surgeon General. Thesis submitted in partial 

 fulfilment of the requirements for the degree of Doctor of Philosophy at Yale 

 University. 



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