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JEAN DAWSON 



results follow a study of the reactions of the snail to food if 

 its physiological state is not previously known. 



TABLE II 

 Reactions of well-fed Physa to a mechanical and a chemical stimulus 



SIMULTANEOUSLY RECEIVED. 



Table III briefly sums up the difference in behavior of the well 

 fed, the fasting and the very well fed snails. A mechanical 

 stimulus does not call forth a food reaction in a well fed snail 

 but if the reaction is first started with food the snail will ingest 

 large quantities of such neutral substance as chalk. A mechan- 

 ical stimulus not only calls forth the food reaction in a fasting 

 snail but the snail fails for several minutes to sense any difference 

 between the chemical that ordinarily causes a positive response 

 and the one that causes a negative response. The very well fed 

 snail on the other hand, does not respond to foods by their odor 

 and gives no indication that it senses some of its former food. 

 Indeed, the power of Physa to discriminate its food substances 

 increases with the amount and, perhaps, variety of food taken. 



