SUMMARY AND CONCLUSIONS 



1. The first and immediate effect of toxic substances 

 upon bacteria is an interruption of their multiplication. 

 Reproduction may be only retarded or it may be com- 

 pletely inhibited, dejDending upon the concentration of 

 the toxic substance. If the concentration is sufficiently 

 low, the cells may not be damaged, the action of the toxic 

 substance on them is reversible, multiplication becoming 

 normal after this substance is removed. Such a reversi- 

 ble inhibition of multiplication, without death, character- 

 izes antisepsis. The condition thus defined is, how^ever, an 

 ideal one, rarely realized; usually a certain amount of 

 slow death accompanies antisepsis. With higher con- 

 centration of the toxic substance, another effect is added 

 which characterizes disinfection. The cells lose their re- 

 productive function permanently because of an irrever- 

 sible reaction of the toxic substance with some cell con- 

 stituent. Permanent loss of reproductive power is to 

 the bacteriologist equivalent to the death of the cell. 



2. The antiseptic action is instantaneous, except with 

 the sulfonamides which permit a fairly normal multi- 

 plication for 2 or 3 generations before the toxic effect is 

 noticeable. The disinfectant action is not instantaneous, 

 but proceeds at a measurable rate, called the death rate 

 (the percentage of cells dying during each unit of time). 



3. As a rule, the death rate is constant throughout an 

 experiment, and this results in a ''logarithmic order of 

 death." In applications to chemical disinfection, the 

 ''deathrate constant" is a valuable tool for the study 

 of the fundamental lethal reaction. 



4. A constant death rate indicates that death is caused 

 by the reaction of one single molecule of the cell with the 



