CHAPTER IX. 



THE DESTRUCTION OF BACTERIA BY CHEMICALS PRACTICAL 

 USE OF DISINFECTANTS. 



MANY chemical substances, when brought in contact with bacteria, 

 unite with their cell substance. New compounds are thus formed, and 

 the life of the bacteria and the disinfecting properties of the substances 

 art' usually destroyed; while in the vegetative stage bacteria are much 

 more easily killed than when in the spore form, and their life processes 

 are inhibited by substances less deleterious than those required to 

 destroy them. 



Bacteria, both in the vegetative and in the spore form, differ among 

 themselves considerably in their resistance to the poisonous effects of 

 chemicals. The reason for this is not as yet clear, but is apparently 

 connected with the structure and chemical nature of their cell substance. 



Chemicals are more poisonous at fairly high than at a low tempera- 

 ture, and act more quickly upon bacteria when they are suspended in 

 fluids singly than when in clumps, and in pure water rather than in 

 solutions containing organic matter. The increased energy of disin- 

 fectants at higher temperatures indicates in itself a probability that a 

 true chemical reaction takes place. In estimating the extent of the 

 destructive action of chemicals the following degrees are usually dis- 

 tinguished: 



1. The growth is not permanently interfered with, but the pathogenic 

 and zvmogenic functions of the organism are diminished attenuation. 



2. The organisms are not able to multiply, but they are not destroyed 

 by antiseptic action. 



3. The vegetative development of the organisms is destroyed, but 

 not the spores incomplete sterilization. 



4. Vegetative and spore formation are destroyed. This is complete 

 sterilization or disinfection. 1 



The methods employed for the determination of the germicidal 

 action of chemical agents on bacteria are, briefly, as follows : 



If it is desired to determine what is the minimum concentration of 

 the chemical substance required to produce complete inhibition of 

 growth we proceed thus: A 10 per cent, solution of the disinfectant is 

 prepared and 1 c.c., 0.5 c.c., 0.3 c.c., 0.1 c.c., etc., of this is added to 

 10 c.c. of liquefied gelatin, agar, or bouillon, or, more accurately, 10 c.c. 



1 Disinfection strictly defined is the destruction of all organisms and their products which are 

 capable of producing disease. Sterilization is the destruction of all saprophytic as well as parasitic 

 bacteria. Practically, however, the two terms are used interchangeably as meaning the destruction 

 of all living bacteria. 



