146 GENERAL PHYSIOLOGY 



at first were evenly distributed throughout the hanging drop, 

 make their way into the tube and collect in it. 



Chemical substances may have an entirely different action 

 from that discussed above ; namely, a germicidal action. This 

 destructive action is frequently spoken of as an antiseptic 

 or disinfecting action. By an antiseptic is meant a sub- 

 stance which interferes with or prevents the growth of bacteria ; 

 while disinfectants are those substances which destroy those 

 bacteria capable of producing infection. All disinfectants, very 

 naturally, possess antiseptic properties, but it does not neces- 

 sarily follow that all antiseptics possess disinfecting qualities. 

 A disinfectant may completely destroy bacteria, and the pro- 

 cess may be complete in the sense of sterilization, or it may 

 be incomplete, the chemical being able to destroy only certain 

 cells. A considerable number of the disinfectants, for example, 

 are readily fatal to the vegetative cells, but are unable^ to kill 

 the spores. The disinfecting action of a substance is influenced 

 by many factors. Some of these factors are resident in the 

 cells themselves and others exist in the external environment. 

 The protoplasmic contents of various bacteria differ to a 

 considerable extent in their resistance to chemical substances. 

 The vegetative cells of some species are twenty times as resist- 

 ant as are others when acted upon by the same disinfectant 

 and under the same conditions. Then, too, the individuals in 

 the same culture differ in their powers of resistance, some indi- 

 viduals being much more resistant than others. 



Certain of the inorganic chemicals are very powerful dis- 



