MICHIGAN ACADEMY OF SCIENCE. 
207 
organisms in the water. It was believed that if the snail were placed 
in water from which such organisms had been removed — that is, filtered 
water — and if reactions were induced by the introduction of food into 
the mouth, any continued reactions after the withdrawal of the food 
would be involuntary on the part of the snail, and therefore the direct 
result of applied stimulation. It would thus be an “unconditional 
reflex.” 
This method was consequently applied, food being used as the original 
essential stimulus. The problem resolved itself into an attempt to 
determine : 
(1) The normal reaction of the mouth parts of the fresh water suail. 
Physa, to a brief application of food as a stimulus. 
(2) The reaction of the mouth parts upon the simultaneous applica- 
tion of food and of another stimulus, such as pressure, to some other 
part of the body. 
(3) The reaction of the mouth parts of the snail when the associated 
stimulus only was applied in the absence of food. 
(4) The possible existence of the power of discrimination, by slightly 
changing the associated stimulus, as for example changing the location 
of the pressure or applying it to some other part of the body. 
(5) The effect of successive stimuli, that is, does the response in- 
crease with repetition of the stimulus or the reverse, and do conditional 
and unconditional stimuli, when repeated, give like results. 
(1) The snails for the work were obtained from a local pond. When 
brought into the laboratory they were in a wild condition, instantly 
retracting into their shells and dropping to the bottom of the aquarium 
if touched or jarred in any way. It was therefore necessary to tame 
them so that they could be readily handled without frightening them. 
This required a considerable amount of time and careful work, inasmuch 
as the requirements of the problem depended upon the normal actions 
or behavior of the animals. More than a hundred of them were placed 
in an aquarium in which water plants were growing, making the 
environment as nearly natural as possible. About twenty specimens of 
approximately the same size were selected for the tests. These were 
placed in smaller dishes containing water plants and abundance of food 
and were handled at intervals and mechanically floated upon the sur- 
face film until they became so tame that they could be transferred 
from one dish to another and variously moved about at the will of the 
operator, apparently without disturbing them. 
They were then divided into two groups, the individuals in each being- 
given a distinguishing mark with waterproof paint especially prepared 
from material which would not injure them. The groups were starved 
for twenty-four hours and were then tested and allowed to feed for 
twenty-four hours. A record was made for each individual during a 
definite number of tests. The individual records show a wide varia- 
tion, but perhaps no 1 more than might be expected from individuals of 
any given species of animal. The averages show much less variation 
than the individual records and give a working basis for the first part 
of the problem. The actual figures are not given at this time because 
sources of error have appeared which make check tests advisable. 
(2) Pressure, by means of a special apparatus (see fig.l), was in- 
