The pitch-discrimination test was the last test in the group series. At its conclusion, and after the measurement of the skin temperature (see p. 249), four of the men were sent downstairs for individual psychological measurements. The remaining subjects were employed for the Du Bois body measurements, the blood test, practice in becoming used to walking on the treadmill, etc. (see program as outlined on p. 59), until the experimenters were to use them.

The psychological apparatus was distributed in three rooms, which open from a common hallway. With the aid of two assistants, it was possible to make such measurements with four of our subjects at the same time, each man serving a total of about 70 minutes. The measurements were grouped in the different rooms, according to expediency. In room A were located Nos. 6, 11, 16, and 17 (strength of grip; continuous discrimination in finding serial numbers; efficiency in traversing the maze; and the clerical tasks). In these tests two men could work in the same room at the same time without disturbing each other. The subjects were located at two well-lighted tables placed some distance apart and not facing each other. The assistant, Mr. J. I. Waldron, whose careful service we were fortunately able to secure, occupied a position between them. The working conditions were made satisfactory to the men. One subject filled out the clerical test blank while the other completed tests Nos. 11 and 16. The time required for each subject to do his particular task was recorded by the assistant in seconds and fractions on a suitable form. The men then exchanged position and tasks. The strength of grip was usually taken after the other tests in room A were completed, and frequently one subject looked on while another subject was being tested. Each subject made a pulse count on himself when he had completed the clerical blank.

Room B contained measurements Nos. 8, 10, and 15 (patellar reflex, word reactions, and finger movements). The general set-up for these three measurements is shown in figure 31, p. 160. They formed a convenient group, since they all relied on the Blix-Sandstrom kymograph for chronographic record. The experimenter tested the subjects individually. The word reactions were always given as the first test, this being followed by the three finger-movement records. Between the finger-movement records there was an interval of one minute. In the first interval the subject was asked for any observations concerning his general condition. In the second interval, or that between the second and third finger-movement records, a pulse count was taken by the experimenter at the wrist. Following the last finger-movement record, the subject changed chairs and reclined in a steamer chair for the patellar reflex measurement, following which a second pulse count was made by the experimenter. The time required to complete the tests in room B was from 17 to 20 minutes. The subject was then sent to room A or C, if he had not previously had the measurements in these places.

In room C, which is the main psychological laboratory, measurements Nos. 12 and 13 were given. The threshold for electric shock was always first and that for visual efficiency came second. There was a shift of position and a slight intermission between the measurements and 8 to 10 minutes devoted to each one. There were, of course, individual differences, and it was not possible to take exactly the same amount of data on each man. When the measurements had been completed or the time interval allowed had elapsed, the subject was sent to another room or upstairs.1 The two measurements were taken by Mr. Edward S. Mills, whose thorough understanding of the apparatus and intelligent cooperation as assistant in psychological investigations during the last few years insured care in execution.

Some latitude in time for testing a particular man was naturally allowed, but in general, a serious effort was made to maintain a schedule, as it was only on this basis that it was possible to test 12 men in such a variety of ways within a period of 3 to 3 1/2 hours.

The measurements made by the group method and the three series of individual measurements just outlined made up the evening psychological session. No effort was made to have the men serve as subjects in identical order each evening, nor was it expedient to give tests in the same order to the individual subjects each evening.

In addition to the measurements made in the evening, a number of tests were made in the morning after the subjects had spent the night in the group respiration chamber. At these morning sessions, also, the subjects were taken in an order which was most convenient to themselves. The distinctive measurements for the morning session were: Nos. 7, 9, and 14, that is, changes in pulse rate with exertion, reaction time of the eye, and speed of eye movement. These were all in room C, and required the attention of an experimenter and an assistant, Mr. Mills. Finger-movement records, pulse counts, and strength of grip records were taken by a second assistant, Mr. Waldron, in room B. The subjects were called, dressed, ate their breakfast, and came to be tested in groups of 3. It required about 20 to 25 minutes for each group. A particular subject began with room B or C, as was convenient for the experimenter. One subject served at a time in room B, two were tested simultaneously in room C - one for the pulse measurements and the other for the eye measurements. The first subjects were ready at 6h30m a. m. When they had completed the measurements at about 7 a. m., they left the Laboratory not to return until the next session, usually two weeks later. The last subjects tested were ready to leave the Laboratory about 8h30m a. m.

The individual measurements as distributed between the evening and the morning sessions and in the three rooms are therefore as follows:

Evening: Room A

6. Strength of grip.

11. Continuous discrimination and reaction in finding serial numbers.

16. Efficiency in traversing a right-angle maze.

17. Efficiency in performing certain clerical tasks. Room B.

8. Latency, amplitude, and refractory period of patellar reflex. 10. Reaction time for speaking 4-letter words.

15. Speed of the finger movements. Room C.

12. Sensory threshold for visual efficiency.

13. Sensory threshold for electric shock. Morning:

Room C

7. Changes in pulse-rate occasioned by short periods of exertion.

9. Reaction time for turning the eye to a new point of regard.

14. Speed of the eye movements. Room B.

15. Speed of the finger movements. 6. Strength of grip.

On the three mornings when walking experiments were made, i. e., January 6 and 28 and February 3, the morning psychological program was omitted, with the exception of strength of grip. This was taken after 5 minutes of sitting following the walking on the treadmill. The regular morning measurements were also omitted on December 20, when the time was given over to taking standard electrocardiograms. -(See p. 393).

A detailed description of the technique and procedure for the measurements used by the individual method is given in the following pages. The measurements are numbered serially, as on page 139, and treated in an order which represents their general increasing complexity.