BACTERICIDAL PROPERTIES 17 



certain organisms is almost immediate, while with others 

 a greater lapse of time is necessary. 



5. Presence of Or<5ANIC jMatter. — Under practical 

 conditions disinfectants are used in the presence of or- 

 ganic matter, and it has been found that considerably 

 higher concentration and greater length of time are 

 necessary for most disinfectants under such conditions. 

 Such organic material as blood, manure, and urine are 

 often present where disinfection and antisepsis are prac- 

 ticed. These contain chemical bodies that unite with the 

 antiseptic used, rendering it inert. It is therefore neces- 

 sary to use enough disinfectant to combine with the 

 organic matter and enough more to act as an antiseptic 

 and disinfectant. This factor will naturally vary with 

 the kind and amount of organic matter present. 



To summarize, then, w^e find that the disinfectant 

 properties of any given chemical depend upon : 



1. Type of organism 



2. Temperature at which it acts 



3. Concentration 



4. Length of time acting 



5. Amount and character of organic matter 



Earlier in this article mention was made of the fact 

 that scientific disinfection was based entirely upon bac- 

 teriological tests. In determining the value of any given 

 disinfectant it therefore becomes necessary to take into 

 consideration each of the five above-mentioned factors so 

 that a comparison of different antiseptics can be made 

 on the same basis. It is necessary that they all act upon 

 the same organism, at the same temperature and con- 

 centration, for the same length of time, and in the 

 presence of the same amount and composition of organic 

 matter. 



