396 COLLOIDS IN BIOLOGY AND MEDICINE 



Cresol is less soluble than phenol and is a stronger disinfectant than 

 the latter. Its solubility in water is so limited that it must be dis- 

 solved with the aid of soaps and similar substances. These are not 

 true solutions; they are manifest emulsions in the dark field (FREI 

 and MARGADANT). It is still an open question whether the effect on 

 bacteria is exerted by an envelopment by the individual cresol soap 

 droplets, thus forming about them a highly concentrated disinfectant 

 film. Another possibility is that the bacteria withdraw dissolved 

 cresol from their environment, and that cresol diffuses from the 

 droplets to an equal extent into the water. 



A group of disinfectants are active even in a dilution in which the 

 substance is no longer chemically demonstrable. According to R. 

 KOCH, interference with the growth of anthrax bacilli is caused by 

 sublimate even in a dilution of 1 : 600,000. According to H. BECH- 

 HOLD and P. EHRLICH* tetrachlor-o-diphenol interferes with the 

 growth of diphtheria bacilli in a dilution of 1 : 400,000 to 1 : 640,000. 

 According to H. BECHHOLD,* 9 tribrom-naphthol inhibits the growth 

 of staphylococci in a dilution of 1 : 250,000. We can understand the 

 effect of such traces of substances if we consider the course of the 

 adsorption curve (see p. 20) in which the distribution between ad- 

 sorbent and solvent occurs in such a way that the dissolved sub- 

 stance is practically completely adsorbed in the weaker concentra- 

 tion, whereas in higher concentrations the distribution approaches 

 that required by HENRY'S law (between two solvents). 



The objection may be raised that the same conditions are fulfilled 

 in a purely chemical combination, to which we may reply that in 

 many instances such a chemical combination must be considered to 

 occur. 



In favor of adsorption, there are two distinct phenomena, inhibition 

 and death. By choosing a suitable disinfectant in sufficient concen- 

 tration and exposure, microorganisms may be completely killed; that 

 is, they cannot under any circumstances be brought back to life. In 

 other cases, it is only necessary to remove the disinfectant, to dilute it 

 or to transfer the germs to another environment, for the germs to start 

 multiplying again; such action is called inhibition. In such a case, 

 we must assume that the reaction between microorganism and dis- 

 infectant is reversible. In killing, the process may be irreversible. 1 



1 I can readily imagine that death may occur in a reversible process if the 

 action of the disinfectant persists for a sufficient length of time to nullify other 

 vital processes. To give a very crude comparison, if a man is drowned, the 

 water cannot be regarded as a poison though it depresses necessary vital proc- 

 esses. A man who cannot be resuscitated after a submersion lasting 5 minutes 

 has fixed no more water in his body than one who has been resuscitated after 2 

 minutes' submersion. 



