336 PHYSIOLOGY OF BACTERIA 



agent in a medium suitable for growth. The same 

 applies, in principle, to death by chemical agents, 

 but it is frequently hard to comply with, since many of 

 the ordinary disinfectants will react chemically with 

 the components of the medium. This reduces the 

 concentration of the acting poison [Kronig and Paul, 

 (1897); Chick and Martin, 1908]. 



Heavy metal salts will react with proteins and form insoluble 

 precipitates. Formaldehyde also combines chemically with proteins. 

 Acids and alkalis will be decreased in their efficiency through the 

 buffer action of the nutrient medium. While it may be possible to 

 find a good synthetic medium for each kind of disinfectant to be 

 tried, it would be necessary to adapt the media to each bacterium, 

 as well as to each disinfectant. This complicates matters to such 

 an extent that for the sake of uniformity, a suspension of bacteria 

 in water seems preferable for studying the general laws of chemical 

 disinfection. 



Removal of Poison after Action. — Experiments on the 

 influence of chemical compounds may be carried out 

 for different purposes. The food industry, in testing 

 the efficiency of benzoate of soda, or of vinegar and 

 spices, is not really interested in the killing of bacteria. 

 Their purpose is fulfilled if the agents under test prevent 

 growth and fermentation. In the disinfection of stools 

 and of sputum, and of animal carcasses, actual killing is 

 intended, and is accomplished without removing the 

 disinfectant from the bacteria. For other purposes, the 

 disinfectant is removed after action, e.g. in the disinfec- 

 tion of hands, instruments, tools, furniture and rooms, 

 and fomites generally. 



There is a great deal of difference in the efficiency 

 of the various methods. The first way, the suppression 

 of growth, shall not be discussed here to any extent, 

 because it is nothing biologically definite, but a mixture 



