186 BARNETT COHEN 



terial spores, Bigelow and Esty (1920) find that the time of steri- 

 lization is increased ten times for a 10° reduction in sterilizing 

 temperature. The Committee on Standard Methods of Examin- 

 ing Disinfectants of the American Public Health Association in 

 its last report (1918), has made reconm:iendations for the inclu- 

 sion of the temperature coefficient as one of the three necessary 

 items in the characterization of disinfectants. 



As has been stated above, the relation between temperature 

 and the speed of chemical reactions is as yet upon an empirical 

 basis, van't Hoff (1896) attempted a derivation from ther- 

 modynamic considerations but obtained no definite solution. 

 Arrhenius (1889) assumed that reacting substances occur in two 

 tautomeric forms, "active" and "passive," and that a certain 

 quantity of heat is involved in activation. He suggests a rela- 

 tion of the form: 



Vi = vo-e 





for the velocities of reaction, 2^0 and Vi, at absolute temperatures 

 To and Ti, the quantity q being the constant of activation. 

 Numerous empirical formulae of the same general form have been 

 suggested from time to time; and that of Snyder (1911) is one 

 that he applied to physiological processes. Tolman (1921) dis- 

 cusses the views that have been held and points to the lack of 

 a real fundamental explanation of the temperature effect in 

 monomolecular reactions. Dushman (1921) and Lewis and 

 McKeown (1921) offer theories of chemical reactivity which 

 appear to be based upon fundamental considerations and include 

 the effect of temperature. 



There is an ever-increasing literature upon the effects of hy- 

 drogen ion concentration' in many biological processes, as a 

 glance at the references quoted by Clark (1920) wiU show. In 

 the field of bacteriology its importance as a controlhng factor 

 is definitely established. This control is exercised in many 

 subtle and unexpected ways — upon the activity of specific 



' In this work, the Sorensen symbol pH is used synonymously for the hydrogen 

 ion concentration. 



