CONCLUSIONS 171 



disinfectant. It seems logical to assume that this all- 

 important molecule is either a gene or a similar master- 

 molecule of the cell division mechanism. Several authors 

 have defined the death of bacteria as a lethal mutation. 

 In the outstanding excej^tional case of chlorine, for 

 which the order of death is not logarithmic, it is prob- 

 able from microscopic observation that the cell membrane 

 is attacked first, and that many membrane molecules 

 must be destroyed before the cell is dead. 



5. Constant death rates permit us to express the ef- 

 fects of temperature and of concentration in simple 

 terms. The death rate increases with increasing tem- 

 perature, and, as a rule, the temperature coefficient for 

 10 degrees C. is between 3 and 5. 



6. The efficiency of disinfectants increases with their 

 concentration, but not in the same manner for all disin- 

 fectants. With formaldehyde, hydrogen peroxide and 

 many other disinfectants, the deathrate constant is ap- 

 proximately proportional to the concentration, but with 

 some others, it is proportional to the square of the con- 

 centration, or to the square root, and with the phenols it 

 increases as the 6th to 8th power of the concentration. 



7. The only standard method for the evaluation of 

 disinfectants is the phenol coefficient which states how 

 many times as powerful as phenol a disinfectant is. As 

 the efficiency of phenol changes with the concentration 

 In an exceptional manner, different from that of prac- 

 tically all other antiseptics, this ratio varies greatly when 

 dilute concentrations are compared. The choice of phenol 

 as a standard is therefore most unfortunate. The range 

 allowed by the Federal Drug Administration Method 

 gives values with a calculated permissible deviation of 

 260%. A new method is projDosed here which gives the 

 death times for any concentration of the disinfectant di- 

 rectly, not merely in comparison with phenol. By this 

 method, the interference of organic matter with disin- 

 fection can also be measured quantitatively. 



