DISINFECTION STUDIES 187 



enzymes, upon toxin production, upon the dissociation of essen- 

 tial foodstuffs and upon the state of aggregation of cellular pro- 

 toplasm. Our present meager knowledge permits us usually 

 to see only the end result in growth, metabolism or death. 



Cohen and Clark (1919) found that the acid limit for the growth 

 of Lactobacillus bulgaricus is not identical with that for fermenta- 

 tion, thus suggesting a possible distinction between bacterial 

 growth and metaboUsm. In the experiments to be reported 

 in this work there is a hint that we might extend this distinction 

 to include bacterial death. 



These factors, temperature and hydrogen ion concentration, 

 have been utilized in the present investigation to study some of 

 the characteristics of that phase of disinfection produced by 

 mild factors, which for want of a better term we have called 

 sub-lethal. 



Beginning with the first systematic studies by Koch (1881), 

 who was later followed by Paul and Kronig (1896), Kronig and 

 Paul (1897), ^ladsen and Nyman (1907), and culminating in 

 the achievements of Chick (1908, 1910, 1912), there has been 

 evolved a theory of disinfection based upon well known principles 

 of physical chemistry. This may be summarized by the dictum 

 of Phelps (1911): "The rate of dying, whether under the influ- 

 ence of heat, cold or chemical poison, is unfailingly found to 

 follow the logarithmic curve of the velocity law, if the tempera- 

 ture be constant." Lee and Gilbert (1918) come to a like con- 

 clusion after a critical investigation. 



On the other hand there are some like Reichel (1909), Loeb 

 and Northrop (1917), Brooks (1918), Peters (1920) and Smith 

 (1921) who urge that the logarithmic process is only an apparent 

 one, and that careful study of the intimate nature of the disin- 

 fection curve will show it to be dependent upon the individual 

 resistance of the organisms. Brooks supports the contention 

 of Loeb and Northrop that bacteria are distributed according 

 to resistance upon a probability curve and that bacteria of low 

 resistance die off first. Since the logarithmic law takes cogni- 

 zance of the number of organisms without regard to the distribu- 

 tion of resistance among them, the operation of this law among 

 bacteria would, so they claim, be an unnatural process. 



