BIOLOGY OF PHYSA 83 



acid for nine or ten minutes before it could be made to close its 

 mouth for an instant, and much longer periods elapsed before 

 the snail closed its mouth for any length of time. It might 

 be thought that the constant application of a chemical such 

 as an acid would render the snail insensitive to it; but this 

 does not seem to be the case in these experiments; in fact, 

 the longer the acid is applied the more sensitive the snail seems 

 to be to it and the less number of applications of the acid it 

 takes to cause the mouth to close. 



c. Experiments on the food reactions of very well fed snails. 



1. A very well fed snail differs from a well fed one in that 

 its chemical sense seems to be blunted. At any rate crushed 

 apple waved over the head of a snail in this condition will not 

 cause the food reflex. It may, however, respond to the apple, 

 if touched to its mouth even though the odor of it failed to call 

 forth a response. 



2. Apple may be eaten while cracker crumbs placed around 

 the snail's head elicit no more response than pieces of chalk do. 



It is a notable fact that the above results with acid and sugar 

 on the snail in its different physiological states can be obtained 

 by onion and apple or cracker, or even by their odor alone. The 

 following results maybe obtained with the onion, cracker or apple. 



a. If onion is brought near a well fed snail which is not at 

 the time giving the food reflex, it does not open its mouth but 

 turns away or curls its head into the shell, according to the 

 strength of the stimulus. If it is giving the food reflex, however, 

 it stops and soon refuses to open its mouth again for some time 

 after the removal of the stimulus. If cracker or apple is given 

 first, the food reflex is started and if onion is then given, the 

 well fed snail will eat it for about two minutes as readily as it 

 did cracker or apple. If, however, onion is offered first, the snail 

 does not respond to either apple or cracker for some tifne there- 

 after. A hungry snail responds equally well to cracker, apple 

 or onion for the first three or four minutes and then there is 

 less and less response to the onion. 



The effect of quinine upon Physa is worthy of note. The 

 hungry animal took the quinine powder into its mouth as it 

 did cracker or sugar for the usual length of time and then fol- 

 lowed short periods of inaction, but upon further application 



