52 
CURT P. RICHTER 
the onset of the large contractions, the main hunger contractions, 
that the animal enters the food box. With the introduction of 
food into the stomach the contractions cease. Once started at 
eating, however, the animal continues until the stomach is filled. 
The activity in the cage following the return from the food box 
is made up entirely of cleansing manoeuvres elicited by the 
various kinds of external stimulation connected with eating. 
The fact that the animal does not enter the food box until the 
onset of the large contractions may be explained in the following 
way: At birth the members of all mammalian species are known 
to have contractions of the stomach almost continuously 
(Carlson). Driven then by these contractions the animals are 
active diffusely and remain active until either stomach contrac¬ 
tions are in some way stopped, or else due to gross exhaustion 
the animals are no longer able to move. They move and toss 
their heads about here and there, suck at everything that happens 
to stimulate their lips, bits of straw, hair of the mother’s body, 
feet and ears of sisters and brothers, and finally the teats of the 
mother. It is only the last of these activities that brings about 
a change within the organism. When the teats touch the lips 
sucking movements are elicited; a warm stream of milk flows 
down the animal’s throat; the stomach contractions are stopped; 
hunger pangs are relieved; the animal lies down and goes to 
sleep. Each time the contraction periods begin again the animal 
becomes active; begins moving about and sucking at everything 
and the whole process is repeated. As this trial and error proc¬ 
ess goes on, the onset of the stomach contractions gradually 
becomes more and more definitely associated with the sucking 
of the teats, becomes the main motor outlet, while the others 
fall into disuse. This process goes on for a time; in the rat it is 
a matter of days (as near as I could determine by observation, 
eight or ten days); in the human infant it is a matter of months 
until the stomach contractions elicit the one reaction of crying 
and actually seeking food. This process is somewhat complicated 
by the fact that the stimulus to activity is not at all times the 
same, for, as was shown above, the stomach contractions vary 
considerably in amplitude, also possibly even in their nature 
