96 BACTERIOLOGY 



there is one fundamental rule always to be borne in mind, 

 viz., it is essential to success that the disinfectant used 

 should come in direct contact with the bacteria to be de- 

 stroyed, otherwise there is no disinfection. 



For this reason one should always remember, in selecting 

 the disinfecting agent, the nature of the materials containing 

 the bacteria upon which it is to act, for the majority of 

 disinfectants, and particularly those of an inorganic nature, 

 vary in the degree of their potency with the chemical nature 

 of the mass to which they are applied. Often the materials 

 containing the bacteria to be destroyed are of such a character 

 that they combine with the disinfecting agent to form insol- 

 uble, more or less inert precipitates; these so interfere with 

 the penetration of the disinfectant that many bacteria may 

 escape its destructive action entirely and no disinfection 

 be accomplished, although an agent may have been employed 

 that would, under other circumstances, have given entirely 

 satisfactory results. 



An antiseptic is a body which, by its presence, prevents 

 the growth of bacteria without of necessity killing them. 

 A body may be an antiseptic without possessing disinfecting 

 properties to any very high degree, but a disinfectant is 

 always an antiseptic as well. 



A germicide is a body possessing the property of killing 

 bacteria. 



Mode of Action of Disinfectants. In the destruction of 

 bacteria by means of chemical substances there occurs, 

 most probably, a definite chemical reaction that is to 

 say, the characteristics both of the bacteria and the agent 

 employed in their destruction are lost in the production of 

 an inert third body, the result of their combination. It is 

 impossible to state with certainty, as yet, that this is in 



