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The Learning Process in a Snail



    IN his well-known experiments (1904), the Russian physiologist Pavlov showed that salivary secretion in a dog, primarily induced by the odour or sight of food, could eventually be induced by a sound or colour which had been for a time synchronised with the primary stimulus. The dog, according to the experiments, was soon able to establish an organic association between the primary and the secondary stimulus. When Pavlov slightly changed the secondary stimulus there was a change in the dog's salivary reaction, and this was taken as evidence of the animal's power to discriminate between stimulii. With noteworthy clear-headedness, Miss Elizabeth Lockwood Thompson has seen how to apply Pavlov's method to a water-snail, Physa gyrina, which glides about in ponds, with foot and mouth upwards, suspended from the surface-film. When a part of the body within a millimetre or two of the mouth is touched with a bit of food, a chewing motion of the mouth-parts is started. With the application of food to near the mouth there was synchronously associated a pressure With a clean glass rod at a fixed distance from the mouth. The next step in the ingenious experiment was to apply tne associated or auxiliary stimulus alone in the absence of food, in order to determine from the presence or absence of reactions whether or not an association had been formed between the two sets of ostimuli. Miss Thompson deserves to be congratulated, we think, on this extension of Pavlov's method, which he himself did not regard as applicable except to a limited number of mammals. It is now possible, along this line of investigation, to test a snail's power of “learning.”

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