things than do the dogs and cats. Considering this and also their close relationship physically to man, it seemed of special interest to discover whether they could learn from example or from being put through certain movements, whether they would manifest the capacity so evident in man and so lacking in the lower animals in general.
I had one monkey for over a year and two others for about four months. All three were of the genus Cebus. The general method of the experiments was as follows: Boxes about a foot square were made with small doors held by all sorts of contrivances. For instance, one was held by a hook, another by a bar, another by a bolt, another by a wire fastened firmly at one side and wound round a nail at the other. A bit of food was put inside such a box and the door of the box left open. The box was then put inside one of the large cages containing a monkey. It would come down, reach into the box and get the food. After this had been repeated a few times the box would be put into the cage, with its door shut. The monkey would try to get in as before. He might chance to operate the simple mechanism that held the door. If, however, he did not succeed of his own impulsive activity I would show him or put him through the movement a few times and then leave him to himself again to see if he had profited by the tuition.
The general result was that they did not profit by the tuition, that they did not gain and use ideas of how to open the doors, but learned only by a process of selection from their own impulses. The meaning and value of this general fact will ajpear in the details of the experiments.
In order that such experiments shall be valid tests of the workings of an animal's mind it is necessary that he surely desire to get into the box, that he be not disturbed by the surroundings in any way that will alter his mental efficiency, and that the experimenter be able to handle him easily without frightening him or taking his attention away from the box. In all cases it is further necessary to make sure that the monkey sees you perform the acts you expect him to imitate, and sees and feels himself make the movements you put him through. These desiderata were obtained by testing the monkeys when hungry and using bits of food of which they were especially fond as the attraction; by experimenting with them after they were quite used to their habitat and to my presence; by getting them into the habit of coming to me and enjoying being handled, having their paws taken, etc.; by showing them the act or putting them through it only when they were attending to the box.
A sample of one of the experiments on the influence of example is the following: The box used was arranged so that the door opened when a brass lover was depressed about an eighth of an inch. The monkey could reach this lever by putting his hand through a hole about an inch
