132 STERILIZATION AND DISINFECTION 
sterilization are disinfection processes. Even with this close relation 
of the process there are certain procedures and reagents which are 
used more as disinfectants than as sterilizing agents. Many of these 
could not be applied to media and some apparatus since some of the 
disinfectant remains after the treatment. 
Disinfection is a chemical process and therefore follows chemical 
laws. Chick (1908) has given the best work on this subject and much of 
her data form the basis upon which our knowledge with regard to 
disinfection rests. The chemical reaction in this case would take place 
between the disinfectant and the bacterium protoplasm. The disin- 
fection process follows the well-known law of physical chemistry—the 
monomolecular law. The same equation may be used provided legi- 
timate substitutions are made in it to make it fit disinfection. 
or 
This may be changed to 
In this equation ¢c, and cg have been substituted for n, and ne the 
numbers of surviving bacteria. For such a discussion, we may define 
the monomolecular law as one governing a reaction between two sub- 
stances where the change in concentration of one may be measured. 
This law seems to be followed in all cases of disinfection when any 
agent is used to destroy bacteria. It is apparent that the rate of death 
is always proportional to the number of cells which are living at any 
given time. This simply means that where there are larger amounts 
of reacting substances, more reaction is secured. Consequently a 
greater d:op is secured in the curve during the first units of time. 
Some objections may be raised against regarding disinfection in this 
light. The bacterial cell must be regarded as a molecule. It is quite 
different since it possesses ‘‘ life ’’ and is surrounded by a membrane. 
It is also necessary to neglect the change in concentration of the dis- 
infectant. At present the disinfectant is usually added in such excess 
that any change which might occur is neglected. 
Different opinions exist with regard to how the disinfection process 
should be explained. For disinfection purposes, a bacterial culture is 
regarded as made up of a uniform population. Hewlett (1909) and 
