ANTISEPTICS AND DISINFECTANTS. 167 



quicklime (milk of lime) requires a contact of several hours to in- 

 sure the destruction of pathogenic bacteria. 



(/) The temperature at which the exposure is made has a 

 material influence upon the result. This is shown by the experi- 

 ments of Henle and of Nocht. As a general rule germicidal activ- 

 ity increases in direct proportion to the increase in temperature from 

 20 C. upward. 



(g) The degree of dilution of the disinfecting agent is also a 

 matter of importance . This is especially true of solutions of acids 

 and alkalies. When a silk thread to which bacteria are attached is 

 suspended in an acid solution the essential point is the degree of 

 acidity, and not the quantity of acid in the entire solution. But if a 

 solution of permanganate of potash, or any other active oxidizing 

 agent, is used, the principal question is not the degree of dilution, but 

 the amount of the disinfecting agent present in the solution used. A 

 grain of potassium permanganate dissolved in two fluidounces of 

 distilled water would probably kill just as many bacteria as if it 

 were dissolved in half a fluidounce, although the time required for 

 disinfection might be longer. 



From what has been said it is evident that the simple statement 

 that a certain agent is a germicide in a certain proportion has but 

 little scientific value, unless we are made acquainted with the condi- 

 tions under which its germicidal action has been tested. 



