90 ATLAS OF BACTERIOLOGY. 



media should always be employed as auxiliaries 

 when we have to deal with the isolation of a bacteri- 

 um from an acid medium. In counting the germs in 

 the air, earth, water, milk, etc., the neutral medium 

 should always be used. 



3. INJURY TO BACTERIA BY CHEMICAL SUB- 

 -STANCES. 



In the presence of an excess of acids or alkalies we 

 have just recognized a factor which exerts an inhibi- 

 tory influence on development, and, in still greater 

 intensity produces death. The most varied chemi- 

 cals act in a similar manner after a certain degree of 

 concentration. The most effective substances are 

 known as antiseptics or disinfectants. 



With Hiippe, we usually distinguish the following 

 degrees of action : 



1. The growth is not disturbed but the pathogenic, 

 zymogenic functions are weakened attenuation, miti- 

 gation. 



2. The organisms can no longer proliferate but are 

 not killed asepsis, kotysepsis. 



3. The vegetative conditions of the micro-organisms 

 are destroyed but not the permanent forms anti- 

 sepsis. 



4. The vegetative and spore forms are killed 

 sterilization or disinfection. 



Inasmuch as the test of the resisting power to 

 chemicals plays a minor part for diagnostic purposes, 

 this section will be treated very briefly. 



The following plan should be adopted in order to 

 determine the minimum concentration of the chemical 



