CHAPTER II 

 INHIBITION OF GROWTH 



Poisons, Germicides, Disintectants, Antiseptics, Preserva- 

 tives. — ^A great number of inorganic and organic bodies will destroy 

 life in comparatively weak solutions. These substances are called 

 poisons if they are considered in their effect upon man and animals. In 

 their application to microorganisms they are generally called germicides 

 (geTm-ki]leis),0T disinfectants if the emphasis is laid upon the prevention 

 of infection rather than upon the actual killing of the microorganisms. 

 Analogous to the general term germicides, the terms bactericide and 

 fungicide are used occasionally. The term antiseptic means a prevention 

 of sepsis which may be accomplished by checking the growth without 

 necessarily killing all microorganisms. The meaning of the word ^re- 

 servative is practically the same, "only the latter is used more commonly 

 in relation to foods, feeding stuffs and preparations of similar origin 

 while the word antiseptic is largely used in relation to microbial diseases. 

 A strict Une cannot be drawn between any of these definitions. A dis- 

 infectant, if diluted, becomes an antiseptic. A strong salt solution is an 

 antiseptic for some organisms and a disinfectant for others. Of the 

 above expressions, germicide is the most definite, but is not so commonly 

 used as the 6thers. 



Mode of Action. — ^The action of a poison upon the cell is generally 

 considered an action upon the protoplasm. The poison is supposed to 

 combine chemically with the ceU plasma producing compounds which 

 interfere with the continuation of the life processes and thus cause 

 death. If the cell has been subjected to the action of the poison only a 

 short time, it can he saved by removing the poison. Bacteria can be 

 treated with mercuric chloride (HgCla) so that they will no longer de- 

 velop if transferred to a fresh medium. If the mercuric chloride is re- 

 moved from the cell by means of hydrogen sulphide, some of the organ- 

 isms may be revived. 



The mode of death through poison is the same as that through 



232 



