80 JEAN DAWSON 



satisfied as they always show a readiness to eat. I term their 

 condition well fed, (2) The second group includes those that 

 had had no food near them for several days. They may be 

 spoken of as in a fasting condition. (3) The third group con- 

 sists of those that have been very well fed in the laboratory. 



In performing the following experiments, each snail was placed 

 alone in a clean bacteria dish filled with filtered tap water. 

 The experiments were performed upon the animal while it was 

 crawling upon the surface film. It was found that this position 

 of the snail was by far the most satisfactory one for the operator, 

 since the action of the mouth could be watched conveniently 

 while the chemical was being applied. When two chemicals 

 were given to the snail, one after the other, the animal was 

 washed off after the first application and removed to fresh 

 water, to insure against any trace of the first chemicals re- 

 maining before the application of the second. A solution of 

 .05% of hydrochloric acid was found to call forth a negative 

 response if used in small quantities. The chemical was applied 

 by dipping a glass probe into it and touching the snail with 

 it in the imrnediate region of the mouth. Granulated sugar 

 was found to give a positive reaction and was applied by placing 

 a granule near the mouth. When onion and apple were used, 

 they were crushed and small pieces laid upon the ventral part 

 of the head, or a probe was first dipped into the juice and then 

 in turn touched to the animal's mouth. 



a. Experiments on the food reactions of well fed snails fresh from the field. 



(i) Mechanical stimuli applied to the mouth or head of a 

 well fed snail, if its jaws were not moving, did not induce the 

 reflex action of the jaws seen in feeding. A stimulus of this 

 nature was given with a glass rod or a piece of chalk applied 

 to the head and on the mouth. 



(2) If the snail chanced to be moving its jaws before the 

 experiment then it would continue to do so, and would not 

 close its mouth when touched or when the chalk was brought 

 in contact with the head. Indeed, it would take particles of 

 chalk that were floating on the film into its mouth and continue 

 to do so for half an hour or more at a time. Thus it is seen 

 that the chalk particles did not start the food reaction, but when 

 the reaction was once started, the chalk was ingested. This 



