TOXICOLOGY AND PHARMACOLOGY 391 



Disinfection. 



By disinfection we understand the killing or rendering harmless of 

 dangerous germs outside of or within the body. Substances which 

 destroy germs living on foods, without being very harmful to higher 

 organisms, are called preservatives. 



For simplicity we shall first consider external disinfection by chemi- 

 cal means. In the process of disinfection a distribution of the dis- 

 infectant between the organism and the medium first takes place. This 

 distribution may occur either in the manner of chemical combina- 

 tion, adsorption or in accordance with HENRY'S law. In the two 

 former cases it is conceivable that even traces of the poison are active, 

 whereas this would be possible in HENRY'S distribution only if the 

 substance is very much more soluble in the bacillus than in its 

 medium. It follows from the ease with which they are stained that 

 surface attraction is of great importance in the case of bacteria. 

 And in fact staining arid disinfection are distinguished only by the 

 fact that in the latter instance the absorbed substance exerts a par- 

 ticular poisonous action on the microorganism. 



If for the present we consider a microorganism only as a small 

 particle without special chemical properties and add to such a hypo- 

 thetical emulsion of bacteria, a dissolved substance, this substance 

 would by reason of the mere surface attraction have a tendency to 

 concentrate on the surface of the bacteria to a greater or less ex- 

 tent, depending upon the nature of the dissolved substance, i.e., 

 the more strongly the given substance diminishes the surface tension 

 of the water, the greater is the concentration at the surface. 1 

 Most bacteria act like a suspension which has been protected by a 

 protective colloid, before being flocculated by neutral salts; they are 

 so changed by boiling or by agglutination that they change from 

 hydrophile to hydrophobe suspensions, which cannot be differentiated 

 physically from kaolin suspensions or the like. The electric charge 

 is that of an inorganic suspension, i.e., negative; it is discharged by 

 agglutinin. All these questions are taken up in detail in the chapter 

 on "Immunity Reactions." 



As the dispersed phase, microorganisms are strongly adsorbed by 

 substances with great surface development. (See Fig. 52.) Be- 

 cause of this adsorption, they are readily held back in fine-pored 

 filters such as Chamberland candles (unglazed porcelain), Berkefeld 

 filters (Kieselguhr), asbestos, wadding or carbon filters. 



1 This conception was originally developed and established by H. BECHHOLD 

 in the "International Congress for Applied Chemistry," London (May to June, 

 1909) (see Kolloid Zeitschr., 5, 22, 1909). 



