em 2. Second from the Right End_

On the completion of problem 1 Sobke was in perfect condition, as to
health and training, for experimental work. He had come to work quietly,
fairly deliberately, and very steadily. His timidity had diminished and
he would readily come to the experimenter for food, although still he
was somewhat distrustful at times and became timid when anything unusual
occurred in the apparatus.

As preparation for problem 2, a break in regular experimentation
covering four days followed the control series of problem 1. On each of
these four days the monkey was allowed to get food once from each of the
nine boxes, both doors of a given box being open for the trial and all
other doors closed. For this feeding experiment, the doors were opened
in irregular order, and this order was changed from day to day.

Systematic work with problem 2 began on May 3, with punishment of thirty
seconds for mistakes and a liberal reward of food for each success.
Early in the series of trials it was discovered that Sobke was likely to
become discouraged and waste a great deal of time unless certain aid
were given by the experimenter. On this account, after the first two
trials, the method was adopted of punishing the animal by confinement
for the first ten mistakes in a trial, and of then, if need be,
indicating the right box by slightly and momentarily raising the exit
door. Every trial in which aid was thus given by the experimenter is
indicated in table 5 by an asterisk following the last choice. In the
first series of trials for this problem, aid had to be given in seven of
the ten trials, and even so the series occupied seventy-one minutes. It
is possible that had no aid been given, the work might have been
continued successfully with a smaller number of trials than ten per day.
But under the circumstances it seemed wiser to avoid the risk of
discouraging and thus spoiling the animal for use in the experiment. It
should be stated, also, that it proved impossible to adhere to the
period of thirty seconds as punishment in this series. For the majority
of the wrong choices confinement of not more than ten seconds was used.

For the second series, given on May 4, the conditions were unfavorable
in that it was dark and rainy, and the noise of the rain on the roof
frightened Sobke. He refused to work after the fourth trial, and the
series had to be completed on the following day. The total time required
for this series