This measurement taken in the same way and employing the same apparatus, with the exception of the electrodes,1 was used in the normal series of 1917. The threshold range shown by the 63 normal men was from 46 to 195 volts. The subjects were distributed in threshold ranges as follows:

50 or below. 1

51 to 75. 3

76 to 100. 13

101 to 125. 23

126 to 150. 16

151 to 175. 5

176 to 200. 2

The distribution is seen to be a fairly normal one, the mode is clearly at 101 to 125 volts, within which range 23 of the subjects came. The average for the whole group was 117.3 volts, with a standard deviation for the series of 63 subjects of 30 volts.

With the above values in mind as normals for initial measurements, we may turn to a consideration of the data for Squads A and B, as shown in tables 177 and 178. For the first experiment, September 29, the 10 men of Squad A show an average of 118 volts as compared to 117 volts for the normal series of 1917. That this close correspondence is not entirely accidental is proved by the fact that Kon, Spe, and Fre of Squad A, whose values are not included in the average, show a similar average of 123 volts. The 10 men of Squad B in their first experiment had an average of 126 volts, the one man whose records are not in the average (Mac) having a value of 101 volts. It appears that in initial measurements of the threshold for electric shock, with the apparatus and technique here employed, a normal average value of about 120 volts may be reasonably expected. Squad A (see table 177) for the nine experiments of October 13 to February 2, has also a total average for the ten men of exactly 120 volts, suggesting that there has been very little, if any, improvement in contrast to the visual threshold results throughout the period of measurements. The averages for the individual subjects, exclusive of September 29, range from 69 volts for Moy to 172 volts for Mon.

1The electrodes were also of the non-polarizable type, but separate vessels were provided for each finger; the vessels being quite small, the level of the solution was adjusted for each subject. The normal measurements were made in the summer and the salt solution was of room temperature. It was unnecessary to warm it by the electric heater.

Table 177. - Squad A - Electrical Threshold And Its Variability

[M. and 8. D. in volts; C. in per cent].

The average individual threshold determinations for the members of Squad B demonstrate no peculiarity which differentiates them from the values which have been discussed for A. The group average for the 5 normal experiments is 115 volts as compared to the value of 126 volts for the first session. This indicates some improvement. The average for the 3 low-diet experiments is 123 volts, which is fairly close to the average for the first experiment.

In connection with these threshold averages, and more particularly with the variability values, a matter of experimental procedure deserves consideration. In the electrical-threshold determination it was desirable to secure an average, if possible, that had statistical significance. With this apparatus, stimuli could be presented about every 2.5 seconds. If one began at a value which was easily felt and proceeded with the series by decreasing the voltage carefully in small steps to that which was the threshold value, it required about 1 minute to reach and pass the threshold. Thus, at best, in the time available not more than 5 to 8 test series could be given. This is a somewhat small number to average. In supplement of the description of procedure, given on page 176, it should be made clear that following a preliminary series to determine the approximate value of the threshold, series lasting about 2 minutes were taken very near the threshold level with an effort to get as many responses in this vicinity as possible. The voltage was increased and decreased very gradually. If the subject responded two or three times in succession the voltage was gradually decreased to a point where he failed. If he failed to respond to two or three shocks which came through to his fingers, the voltage was gradually increased. In other words, a large number of shocks in increasing and decreasing series were given in succession. The subject, realizing that the shocks were all to be very close to his limit, concentrated his attention at those moments when the shock might be expected and responded to every one which he felt. The voltage of every shock with response or failure to respond was recorded. In elaborating the records, the average between successive voltage records when the subject responded in one case and in the next case failed to respond, was arbitrarily considered a threshold determination. For example: if a man responded to a shock voltage of 104 volts and had been responding to shocks of this strength, or stronger, and then failed to respond to a shock of 100 volts, the threshold determination was considered the average of 104 and 100, or 102 volts. Usually about 20 such determinations would occur in the records taken with a subject in the test period of one evening.

Table 178. - Squad B - Electrical Threshold And Its Variability

[M. and S. D. in volts; C. in per cent].

The average standard deviation for the individual series of determinations on a single subject (see tables 177 and 178) is about 7.5 volts. There are rather wide variations from this, that is, with Squad A they range from 2 to 20 volts. Pea has the largest average standard deviation (10.8 volts) of any man in Squad A. The smallest is consistently found with Moy (4.3 volts), whose threshold was also the lowest average for the group. Van and Sch, of Squad B, have standard deviations of 11.6 and 11.3 volts, as averages for the reduction period. Their thresholds were, however, much higher than that for Pea, being 145 and 169 volts, as compared with 100 volts. The standard deviation is usually about 6.5 per cent of the average threshold value. Squad B show slightly less than this, particularly in the average for the five normal experiments, the percentage for which is 4.8. The exceptional case, in the two squads, is that of Pea in Squad A, with an average coefficient of variability of 11.1 per cent for the low-diet period. It is exceptional to find any other of the 25 subjects who comprised these two squads showing a variability of as much as 10 per cent on any date. The small average variability of both squads in their first experiment is due to the much smaller number of threshold determinations that were made on these dates, when the method was not the same as described in the paragraph above, but was identical with that used in the normal series of 1917. The small variability within any individual series of threshold determinations makes this measurement compare very favorably with any sensory threshold measurement with which we are familiar.

The fluctuations of the two sets of results throughout the group of experiments are shown in figure 116. First it may be noted that the standard deviation and coefficient of variability are practically stationary from first to last and are at very nearly the same level for both squads, tending to be a little smaller with Squad B. There is a slight increase in the standard deviation for October 27, Squad A, apparently due to unusually large deviations with Tom, Vea, Pec, and Mon. Both squads show one marked depression (higher threshold) during the period of the experiment. In the case of A this occurred at the first reduction date, October 13, when the average was 138 volts, as compared to the former average threshold of 118 volts, a rise in the threshold of 17 per cent; this change is three times as large as the average standard deviation. Seven of the 10 subjects show in their averages this change to a higher threshold at the time of the second experiment. It is of interest to compare this high electrical threshold on October 13, the first experiment after food reduction began, with the high visual threshold on the same date. (See figure 115.) There are two much smaller depressions in the curve, that is, on November 24 and February 2, but in general, a very even level obtains which is near that of the first and normal (September 29) experiment. Squad B began high at 126 volts, for October 6, which was largely due to the abnormally high threshold found for Fis of 228 volts. This was a value higher than any found among the 63 normal subjects of the series of 1917 and considerably higher than succeeding values with this subject, although his general average is in the neighborhood of 190 volts, the limit of the supposedly normal range. Hence it seems that the improvement shown between the first and second experiments is partly to be discounted as an individual peculiarity. The date of January 5 has previously been noted in other measurements as showing results for Squad B somewhat below their average. The first two experiments during the low-diet period of Squad B, particularly the second one, show a markedly higher electrical threshold than even that of January 5, which is itself higher than that for the three previous dates. The change is very similar to that which occurred in the second experiment with Squad A. On the last date for Squad B, January 27, the normal level was reached, but Squad A was not quite at their normal level in the last experiment.

Fig. 116. - Electrical threshold averages and variability. Solid line curves represent Squad A, and broken curves Squad B.

The data with both squads appear to indicate that, coincident with the beginning of food reduction, the electrical threshold was increased in the neighborhood of 15 per cent, while the standard deviation and percentage of variability show no concomitant change. Threshold determinations on Squad B indicate what might reasonably be expected, i. e., some improvement with practice. It would be surprising if the physiological threshold were reached without practice in this case of electrical stimulation. Squad A shows no such improvement with practice, and this lack we associate with the reduced diet.