114 EFFECT OF CHEMICALS ON BACTERIA 



preparations of the coal-tar acids exhibit active Brownian motion. 

 Often the bacteria are considerably larger than the mean diameter 

 of the emulsified particles. These bombard the bacteria and in this 

 way frequently bring them into intimate contact with the undiluted 

 particles of the disinfectant, which would not occur in solutions. 

 Emulsions act upon bacteria first through physiochemical adsorp- 

 tion and second through chemical combination. But other particles 

 held in suspension also possess this power of adsorption, and hence 

 the strength of emulsions is rapidly reduced. Thus the value of 

 phenol is barely impaired by the presence of organic matter in solu- 

 tion, whereas emulsified disinfectants are reduced to one-third or 

 one-half of their original value. 



Disinfectants of the Chlorin Group. To this group belong many 

 of the more active disinfectants. They are all characterized by a 

 chemical instability in the presence of organic matter. The mem- 

 bers of this group contain active chlorin in distinction to inert 

 chlorin, such as that in common salt. The phrase "active chlorin" 

 does not, however, necessarily imply that free chlorin is contained 

 in the substance or liberated by it. The active agent may be hypo- 

 chlorous acid or some other compound containing chlorin. 



It used to be assumed that they acted mainly by the liberation 

 of nascent oxygen. Hypochlorous acid decomposes thus : 



4HC1O = 2H 2 O + 2C1 2 + O 2 



% \/\^ \_s 



The chlorin then reacts with water, liberating more nascent 

 oxygen: 



2C1 2 + 2H 2 O = 4HC1 + O 2 



Dakin, however, defines a substance as possessing active chlorin 

 when it will part with chlorin either free or combined in such a way 

 that it can effect the chlorination of bacteria and other proteins. 



All proteins are made up of amino-acids in which the amino- 

 group of the one has reacted with the carboxyl group of the other 

 with the elimination of water. This gives imino NH groups. It 

 is assumed by some that the chlorin replaces the hydrogen in this 

 group, thus: 



R 



H C NH 2 

 2C1 = C = O + HC1 



NCI 

 H C COOH 



