Physiological economy in nutrition, with special reference to the minimal proteid requirement of the healthy man / an experimental study

by R. H. Chittenden

Finally, attention may be called to the photographs of the men, taken just prior to the close of the experiment, from which may be gained some idea of their physical condition so far as it can be judged by external appearance. Certainly, there is no indication in these photographs of any lack of bodily vigor. On the contrary, there is good muscular development, without any undue amount of fat, and indeed every indication of a good bodily condition, coupled with that appearance of quickness and alertness that belongs to the well-developed man, in a state of physiological balance. The photographs scattered through this section of the book, showing the soldiers at work in the gymnasium, likewise give some idea of the lighter forms of exercise they followed each day in the training of bodily movements.

What now is to be said regarding the nervous condition of the men; i. e., their ability to respond to stimulation or, in other words, their mental quickness or reaction time? To study this question, the soldiers were sent with regularity to the Yale Psychological Laboratory, where their reaction time was studied with great care. The results of this investigation are contained in the following report made by Dr. Charles H. Judd, in charge of the Yale Psychological Laboratory.

REPORT ON REACTION TIME.

In order to test the quickness of the members of the Hospital Corps Detachment, and to determine whether the changes in diet affected in any way their ability to respond promptly to sensory stimulation, each man was carried through a series of reaction experiments at the Yale Psychological Laboratory. The method of the experiments was that regularly employed in simple reaction time experiments. The person whose reaction time is to be measured is seated in a comfortable position with his finger pressing on an electric key. He is told that he is to lift his finger from the key as quickly as possible when he hears a given sound-signal. The sounder which produces this signal and the electric key are placed in a circuit with a standard time-measuring apparatus—the Hipp Chronoscope. This chronoscope is arranged so that it begins to record the instant the sound is given and stops the instant the reactor lifts his finger. The dial of the chronoscope shows in thousandths of a second (hereafter designated by the technical term sigmas) the time that elapses between the sound to which the reactor is to respond and the movement of response. The chronoscope was tested at frequent intervals by means of a standard pendulum and errors in the record are well under two sigmas.

The time which is measured by this method is occupied chiefly by nervous processes. The following factors may be specified: First, the auditory organ is aroused by the sound; second, the afferent nerve transmits the stimulation to the central nervous system; third, the central nervous system carries the energy to the motor nerves; fourth, the efferent motor nerves transmit the stimulus to the muscles; and finally, some time is required by the muscle for its contraction. It will be seen, accordingly, that the chief factors of a reaction are nervous processes, and since the external conditions of successive reactions are in all respects uniform, any variations in the time of a given person’s reactions may be regarded as indicating variations in the nervous condition of the reactor. In view of the instability of nervous conditions, it is necessary to eliminate any slight or merely temporary fluctuations by taking each time a given reactor is tested a series of reactions. For this reason, a series of ten reactions was taken with each of the men every two weeks during November, December, and January. After an interval of two months, namely, on March 30, 31, and April 1, two final series were made with each man.

The results are presented in tables 1 to 5. The dates in the first column indicate the day on which each individual set of ten reactions was taken. The second column presents the averages of each ten reactions in sigmas. The third column gives the mean variations of the various single reaction times from the average. The fourth column gives the variations of the day’s average, recorded in column 2, from the general average of that individual for all his experiments. These general averages are presented in table 6. At the bottom of each complete column of averages will be found the group average. This quantity is obtained by averaging the results from all the members of the squad for periods of, approximately, two weeks.

The mean variations in the third column make it clear that the subjects did not settle down into what could be regarded as trained subjects. Trained subjects are expected to give mean variations which are consistently within the limits of 10 per cent of the average. While there are, of course, instances in which the mean variation falls within this limit, there is no consistent exhibition of the regularity indicative of thorough practice. This fact is further confirmed by a comparison of the results of March 30, 31, and April 1 with those of the earlier months. At the end of March, all effects of practice in November, December, and January, except the most general, may be regarded as having disappeared; and yet the averages and variations for the March and April dates resemble closely those of the month immediately preceding and also those of November. The effects of practice may, accordingly, be regarded as insignificant.

This lack of special training accounts for the large variations which appear in some cases. As is usual in reaction experiments, the signal to which the reactors were to respond was in each case preceded by about two seconds by a bell signal to arouse attention. Conditions were thus rendered as nearly uniform as possible, but the variations indicate in three or four cases exceptional lapses of attention. Such exceptional cases can be eliminated without prejudicing the final validity of the results by substituting the median for the averages. In table 7, the medians are grouped together and show even more than the tables of average the absence of any general variation during the period of the tests.

The obvious conclusion from these tests is that the quickness of the members of the squad underwent no general change during the whole period covered by the test. Individual members showed variations from time to time, but these variations are clearly accidental in character, for they show no regular tendencies and are in no way related to the changes in the character and amount of the diet.

(Signed) Charles H. Judd.