e curve is determined chiefly by the first
series per day. The extreme irregularities of this curve are most
interesting and puzzling, as are also the variations in the daily ratios
of right to wrong first choices. Three times in the course of the
training, this ratio rose to 1 to 9, or higher. The causes for such
extreme variations are not easily enumerated, but a few of the most
obvious contributory causes are variations in the weather, especially
cloudiness or fogginess, which rendered the apparatus dark; variations
in the degree of hunger or eagerness for food; differences in the
activities of the animals in the cages outside of the laboratory
(sometimes they were noisy and distracted the subject), and finally,
differences in the physical fitness and attitude of the animal from day
to day.

The more or less incidental behavior in connection with this experiment
more strongly than the statistical results of the work on problem 2
indicate the existence of imagery. That ideas played a part in the
solution of the problem is probable, but at best they functioned very
ineffectively. The small number of methods used in the selection of the
right box, and the slight variations from the chief method, that of
choosing the first box at the right end and then the one next to it,
apparently justify Doctor Hamilton's characterization of this monkey as
defective.

[Illustration: FIGURE 19.--Error curves of learning for the solution of
problem 2 (second box from right end).]

_Problem 3. Alternately First at Left and First at Right_

Following the control series given in connection with problem 1, an
interval of rest lasting from August 12 to August 19 was allowed in
order that Skirrl might in part at least lose the effects of his
training and regain his customary interest in the apparatus by being
allowed to obtain food easily instead of by dint of hard labor,--labor
which was harder by far, apparently, than physical activity because it
demanded of the animal certain mental processes which were either
lacking or but imperfectly functional. The difficultness of the daily
tasks appears to be reliably indicated by the tendency to yawn.

Systematic work on problem 3, which has been defined as alternately the
first door at the left and the first door at the right of the group, was
begun August 19, and for nine days a single series of ten trials per day
was given. Work then had to cease because of the experimenter's return
to