CHAPTER XI 



EFFECT OF CHEMICAL ENVIEONMENT UPON 

 MICROORGANISMS 



THERE are four distinct and relatively important 

 methods by which the chemical environment may influ- 

 ence microorganisms: motile bacteria may be influenced 

 in their direction of movement, molds and filamentous 

 bacteria may be influenced in their direction of growth, 

 all types of microorganisms may be influenced as to their 

 rapidity of growth, and as to their rate of death under 

 unfavorable conditions. 



EFFECT OF CHEMICALS ON DIRECTION OF MOVEMENT 



It has previously been stated (Chapter IX) that the 

 effect of any external agency upon the direction of move- 

 ment of an organism is termed a taxy. When the agent 

 influencing such direction of movement is a chemical, the 

 phenomenon is termed chemotaxis. 



Chemotaxis may be most readily demonstrated by 

 .immersing the tip of a fine capillary glass tube partly 

 filled with a solution of beef extract or peptone, in a drop 

 of water containing numerous motile bacteria. Within 

 a short time most of the bacteria in the drop will be 

 found moving about the tip of the tube, and many will 

 have entered. The chemical in solution has been passing, 

 by diffusion, out through the water. The bacteria appar- 

 ently tend to swim in the direction of the greater con- 

 centration. Such a phenomenon of attraction may be 

 termed positive chemotaxis. Some chemicals may exert the 

 reverse influence, that is negative chemotaxis. In general 



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