110 MOLAR AGENTS AND PROTOPLASM [Ch. IV 



results of contact upon protoplasm is modification of move- 

 ment, — momentary quiet, followed by contraction. Rapidly 

 repeated shocks lead to a summation of responses called teta- 

 nus. Slowly repeated shocks may lead to acclimatization to 

 contact. Finally, the direction of locomotion is in some cases 

 controlled by contact ; many organisms move from the touch- 

 ing body — negative thigmotaxis ; others may face the impact 

 of flowing water or keep close, as though attached, to the rigid 

 surface — positive thigmotaxis. If the changed chemical con- 

 dition following contact be called the "response," then all 

 changes wrought by contact on protoplasm may be considered 

 as responses. 



LITERATURE 



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