was seventy-eight minutes.

The work on May 6 was distinctly better, and the animal's behavior
indicated, in a number of trials, definite recognition of the right
door. He might, for example, make a number of incorrect choices, then
pause for a few seconds to look steadily at the doors, and having
apparently found some cue, run directly to the right box. No aid from
the experimenter was needed in this series.

On the following day improvement continued and the animal's method of
choosing became definite and fairly precise. He was deliberate, quiet,
and extremely business-like. The time for the series was thirty-one
minutes.

The period of punishment was increased on May 12 to thirty seconds.
Previously, for the greater number of the trials, it had been ten to
fifteen seconds. This increase apparently did not disturb the monkey,
for he continued to work perfectly throughout the series, although
making many mistakes in spite of deliberate choices and the refusal of
certain boxes in each trial.

An interesting and significant incident occurred on May 13 when at the
conclusion of trial 5, Doctor Hamilton came into the experiment room for
a few minutes. Sobke immediately stopped working, and he could not be
induced to make any choices until Doctor Hamilton had left the room.
This well indicates his sensitiveness to his surroundings, and his
inclination to timidity or nervousness even in the presence of
conditions not in themselves startling.

Work was continued thus steadily until May 28 when, because of the
failure of the animal to improve, it seemed wise to increase the period
of confinement as punishment to sixty seconds. In the meantime, it had
sometimes been evident that Sobke was near to the solution of his
problem. He would often make correct choices in three or four trials in
succession and then apparently lose his cue and fail utterly for a
number of trials.

After June 1, in order to hasten the solution of the problem, two series
per day were given. In some instances the second series was given almost
immediately after the first, while in others an interval of an hour or
more intervened. It was further found desirable to give Sobke all of his
food in the apparatus. When the rewards obtained in the several trials
did not satisfy his hunger, additional food was presented, on the
completion of the series of experiments, in one or more of the food
cups. On days marked by unwillingness or refusal to work, very l