DISINFECTANTS 91 



Formaldehyde reacts very promptly with the amino 

 groups of proteins. (This reaction is used in the quan- 

 titative determination of amino groups.) Naturally, 

 such proteins are then incapable of any physiological 

 function. 



6. Oxidizing Agents. The two best known 

 oxidizing compounds are hydrogen peroxide and per- 

 manganate. They react very differently, however. Per- 

 oxide does not attack proteins or other organic matter 

 readily, but in tissues it is destroyed by the catalase. It is 

 a somewhat more efficient disinfectant than formalde- 

 hyde, and resembles the latter by acting proportion- 

 ately to its concentration, the concentration exponent 

 being approximately 1. Permanganate reacts prompt- 

 ly with organic matter, changing to the inert brown 

 MnOa and thereby losing its efficiency. In pure water, 

 it is more efficient than peroxide, but its usefulness is 

 greatly limited whenever organic matter is present. 

 The concentration exponent of permanganate is approx- 

 imately 4, indicating a rapid loss of power by dilution. 



The lethal reaction with hydrogen peroxide is prob- 

 ably an irreversible oxidation of some vital protein. 

 This oxidation is not due to nascent oxygen liberated by 

 the catalase in the bacterial cells, for the streptococci 

 and lactobacilli which do not contain catalase are nev- 

 ertheless killed by peroxide. 



The rate of oxidation of various chemical substances 

 by hydrogen peroxide is greatly accelerated by the si- 

 multaneous presence of small amounts of Fe+++ and 

 Cu++ ions, and Dittmar, Baldwin and Miller (1930) 

 found this to be true also for disinfection. With 0.1 

 millimol each of Fe2( 804)3 and CuSOi, the phenol co- 

 efficient of hydrogen peroxide increased with Bad. coli 

 from 0.014 to 1.4, and with Staph, aureus from 0.012 

 to 1.2. A combination of potassium dichromate with 

 cobaltous or manganous sulfate produced the same re- 

 sult. 



