90 DISINFECTANTS 



Of the cyclic alcohols, phenol is the best known, but 

 the cresols, thymol, resorcinol, etc., are even stronger 

 disinfectants than phenol. One of the early attempts 

 at explaining the action of phenol is that of Reichel in 

 1909. He showed that phenol dissolves in coagulated 

 serum albumin, and that the fraction of phenol going 

 into the albumin can be increased by the addition of 

 salt. Salt also increases the disinfecting power of 

 phenol, and the death times with various NaCl con- 

 centrations increase in proportion to the partition co- 

 efficient of phenol between water plus salt, and albumin. 



This not only explains the effect of the salt, but proves 

 that the lethal action is brougli.t about only by the pro- 

 tein-dissolved fraction of the jDhenol. The lethal re- 

 action itself remains unknown. Denaturation would be 

 the simplest assumption, but we know that some pro- 

 teins are not readily denatured by the higher alcohols. 

 Phenol and thymol are frequently used in experiments 

 with enzymes to prevent bacterial action; the denatura- 

 tion of enzymes (which are proteins) by these com- 

 pounds must therefore be very slow. Of course, this 

 refers only to dilute solutions, and their rate of disin- 

 fection (and perhaps of denaturation generally) in- 

 creases as the 6th or 7th power of the concentration. A 

 doubling of the concentration would make denaturation 

 2*^ = 64 times as rapid. As stated above (p. 72) the 

 high concentration exponent and its change with tem- 

 perature make it appear possible that phenols are mere- 

 ly catalysts speeding up some natural deterioration 

 which is normally so slow as to be balanced by the cell's 

 repair mechanism. 



5. Formaldehyde. Formaldehyde is the only 

 aldehyde known to have a strong disinfectant power, 

 though not for all organisms ; molds are not very sensi- 

 tive to it. It has one outstanding property, namely, 

 it retards multiplication in very great dilution (see p. 

 129). 



