78 DISINFECTANTS 



cient. McCuUoch found for formaldehyde {n = 1) the 

 following concentrations equally efficient: At 2°, 5%; at 

 20°, 2.5% ; and at 40% 0.5%. This gives Q^s = 2 and 

 Q20 = 5, and consequently Qio = 1.5 and 2.2 respectively 

 for the two ditferent intervals. 



The large majority of experiments on the role of tem- 

 perature in disinfection indicate that the effect is similar 

 to that on chemical reactions. The temperature coeffi- 

 cients average about 2. Often they are very much high- 

 er. Rarely are they consistently less than 2, and if so, 

 this also can usually be explained on the basis of a chem- 

 ical phenomenon, as in the case of alkali whose action 

 is not affected much by temperature. 



The general trend of results is thus in conformity with 

 the explanation that disinfection is due to a chemi- 

 cal reaction of the disinfectant with some cell con- 

 stituents. It excludes the explanation of the logarithmic 

 order by a graded rate of diffusion because a tempera- 

 ture increase of 10 degrees would certainly not be suf- 

 ficient to double the rate of diffusion. But some observa- 

 tions have been recorded which remain unexplained, as 

 e.g., the higher temperature coefficient of very young 

 cells as compared with old ones (Chick, 1910). A careful 

 study in the light of the latest knowledge of temperature 

 effects in biology seems necessary to clarify the role of 

 temperature disinfection. 



TEMPERATURE COEFFICIENTS OF LIFE AND DEATH 



The above-mentioned experiments on the influence of 

 temperature on death processes contain a fact of impor- 

 tance for the interpretation of temperature effects on 

 life processes. Most organisms cease to grow when their 

 temperature is lowered to a few degrees above the freez- 

 ing point of water or cell sap. This cessation of growth 

 is not abrupt. If growth ceases at 5°, it is still exceed- 

 ingly slow at 10° and not very rapid at 15°. The tem- 

 perature coefficient between and 5° is infinite, between 



