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65°. Below 50° she tended to seek shelter, and shivering indicated her unfavorable condition; and similarly at temperatures above 70°, and especially in the direct sunlight, she tended to become quiescent.

If this section has given the reader the impression that conditions of work were other than highly favorable at Shady Nook I have failed in my attempt at effective description, for the trying circumstances, although important enough for mention, seemed rather to stir the interest and determination of Congo and the experimenter than to discourage them.

IV

MEASURES OF ADAPTIVITY OF BEHAVIOR

The experimental inquiry of which this is an account began January 5, 1926. On the morning of that day the grill described on page 30 had been installed and other preparations made. It was my plan and desire to begin work by presenting to Congo some relatively simple problem. Degree of coöperation, industry, and energy could not be predicted, but I assumed that for the reward of much desired food she might be induced to work for at least a few minutes. The use of a stick as tool or instrument with which to obtain desired food was selected as the initial problem.

Although strictly chronological account of observations is for many reasons desirable, I shall in the following pages depart somewhat from it in order to condense the description. The departures, however, are in the direction merely of the grouping of closely related problems. This compromise between the strictly chronological order and the logical seems to be indicated by the plan of work as well as by the results obtained. The reader, however, must constantly bear in mind that the experimental situation steadily became more complicated as new problems were presented to Congo. At the outset I had slight hope that she would work effectively more than thirty minutes at a stretch, but instead she proved very nearly inexhaustible in her interest in experimental situations and her patience in trying to meet them properly. Whereas I had assumed that most of my time might be devoted to planning and preparing experiments, I shortly discovered that I could present one problem after another for as many as four or five hours with no appreciable lessening in Congo's interest or activity if she was reasonably successful in obtaining the desired reward. Starting with one problem per day the number was gradually increased to eight, and as each problem required the setting of an experimental situation, followed by period of observation and the recording of results, we were

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kept very busy from nine a. m. to at least one p. m. with eight problems.

In order that the reader may have a general view of the more important experimental situations used to measure Congo's intellectual and affective responses and adaptations, the following list is given with the date, hour, and, whenever significant, the duration of each trial. The problems are arranged in order of presentation and the list of dates indicates not only this order but the number of presentations and the succession of problems for a given day. The experiments were always conducted in the morning beginning at eight fortyfive to nine o'clock and continuing in accordance with the number of problems to as late as two p. m.

List of problems with dates of presentation

1. Shelf and stick.

Jan. 5, 12:15, 60'; 7, 9:00, 60'; 8, 9:15, 60', 12:10, 2'; 9, 8:50, 15'. M. p. r.* Jan. 19 and Feb. 1.

2. Diagonal rope.

Jan. 7, 10:18, three trials in an hour.

3. Hooked rope.

Jan. 8, 10:20, 20', 10:55, 60'; 10, 9:21, 17'; 11, 9:32, 4'; 12, 9:50, 4'; 13, 9:13, 1' 15"; 14, 9:20, 1' 30"; 15, 9:35, 30"; 16, 9:15, 30"; 17, 9:40, 30". M. p. r. Jan. 19.

4. Platform and stick.

Jan. 8, 12:12, 3′; 9, 9:06, 15'; 10, 9:03, 15′; 11, 9:12, 15'; 12, 9:25, 15'; 13, 8:55, 15'; 15, 9:15, 15'; 16, 9:00, 12'; 17, 9:42, 8'; 18, 11:02, 23′; 20, 10:40, 15'; 21, 9:45, 15'; 22, 9:10, 21'; 23, 9:15, 9'; 25, 10:00, 60'; 26, 9:15, 10'; 27, 11:35, 10'; 28, 12:20, 5'; 29, 9:17, 53'; 30, 9:10, 7', 9:47, 8', 12:15, 2. M. p. r. Jan. 19 and Feb. 1.

5. Pull rope.

Jan. 8, 12:45, 12', 12:57, 30'; 9, 10:10, 3', 10:15, 3'; 10, 9:45, 1'; 11, 9:38, 1'; 12, 10:12, 1' 30"; 13, 9:15, 30"; 14, 9:50, 5′ (estimated); 15, 10:25; 16, 9:42; 17, 10:15. M. p. r. Jan. 19.

6. Milk bottle.

Jan. 9, 10:00, 2'; 29, jar instead of milk bottle.

*M. p. r. stands for motion picture record.

7. Buried food jar.

Jan. 10, 11:00, 30'; 11, 10:55, 15'; 12, 11:03; 13, 10:26, 20′; 14, 10:00, 30′′; 15, 10:20; 16, 10:00; 17, 10:10. M. p. r. Jan. 19.

8. Suspended food and stick.

Jan. 10, 10:35, 5′; 11, 10:20, 30′; 12, 10:30, 30′; 13, 9:43, 15'; Feb. 3, 10:08, 2'; 4, 9:48, 1′ 30′′.

9. Pipe, wire, and stick.

Jan. 11, 11:30, 3′; 12, 11:46, 12′; 13, 10:08, 15′; 14, 9:35, 15'; 15, 9:55, 25'; 16, 9:26, 14'; 17, 9:53, 16'; Feb. 3, 10:27, 13′. M. p. r. Jan. 19.

10. Suspended food and boxes.

Jan. 14, 11:19, 30'; 15, 10:50, 40; 16, 10:07, 30'; 17, 9:03, 16'; 19, 10:55, 30'; 20, 10:08, 30'; 21, 10:10, 30'; 22, 9:43, 30′. M. p. r. Jan. 19 and Feb. 1.

11. Hasp and padlock.

Jan. 15, 12:48, 45'; 16 to 28 inclusive, daily. M. p. r.
Jan. 19.

12. Spring bolt box.

Jan. 17-18, 20-22, 23, box inverted.

13. Hammer and nail imitation.

Jan. 18.

14. Delayed response, multiple-choice apparatus.

Jan. 21, 11:00; 22, 10:25; 23, 10:25, 11:30; Feb. 2, 10:45; 3, 10:45; 4, 10:20. M. p. r. Feb. 1.

15. Identical object, multiple-choice.

Jan. 23, 10:25. M. p. r. Feb. 1.

16. Box imitation.

Jan. 23, 11:00, 20′; 26, 9:20, 22′; 27, 9:50, 33'; 28, 9:14, 16; 30, 9:20, 4′.

17. First object to left, multiple-choice.

Jan. 23, 11:30.

18. Mirror.

Jan. 25, 11:05, 5'-8'; 26, 12:30, 5'-8'; 27, 12:02, 5'-8'; 28, 12:05, 5'-8'; 29, 11:00, 5'-8'; Feb. 3, 11:50, 5'-8'. M. p. r. Feb. 1.

19. Arm and leg reach.

Jan. 26; 28; Feb. 3. M. p. r. Feb. 1.

20. Wound chain.

Jan. 26, 10:40, 55'; 27, 10:30, 60'.

21. Box and weight obstruction.

Jan. 26, 11:26, 30'; 27, 9:10, 30'.

22. Middle object, multiple-choice.

Jan. 28, 10:30; 31, 11:16; Feb. 2, 10:45.

23. Box stacking.

Jan. 30, 10:01, 1′, 10:15, 30′; 31, 9:25, 30′, 10:15, 22′;
Feb. 2, 9:56, 30'; 3, 11:55, 1'; 4, 10:00, 4'. M. p. r.
Feb. 1.

24. Hidden stick.

Jan. 31, 10:00, 2'; Feb. 1, 9:05, 10'; 2, 9:27, 2'; 3, 9:30, 30; 4, 9:20, 1'.

The more or less problematic situations arranged to reveal the nature and extent of Congo's adaptability logically fall into three groups: (1) the use of objects as appliances or tools, as for example in the stick and box problems; (2) the manipulation of environment, as in the several rope problems and in the multiple choice, and (3) the modification of environment, as in the buried food problem. It was my endeavor to select from previously used methods, or to devise, simple experimental situations which should differ widely in type of adaptive response required and in complexity or difficulty for the gorilla. Many of the situations which I employed are described by Hobhouse (19) to whom I gratefully acknowledge my exceptional indebtedness.

With the thought that the use of objects as tools might be the simplest and most effective way to exhibit at once the animal's acquisitions and resourcefulness, I planned a series of problems involving the utilization of sticks or boxes and covering a wide range of requirement. That my plans were completely upset by Congo is made clear in the following description of her behavior.

A. THE STICK AS INSTRUMENT

As soon as general preparations for experimental work had been completed on the morning of January 5, a wooden shelf was placed at the south end of Congo's cage, sloping from the wall of the adjacent study to the cage at an angle of about fifteen degrees. The cage end of this shelf was slightly below the 10 by 10 inch door described on page 30 as feeding door. Nailed to the shelf at either side of the feeding door and extending from cage to study were strips of wood which served as guards to prevent food placed on the shelf from rolling off

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