1062 The American Naturalist. [December, 
physiological means. During the four days and three nights of the test 
they were engaged, as far as possible, in their usual occupations; their 
meals were of the customary kind, and were taken at the ordinary 
times, with the addition of a light lunch at about midnight. At inter- 
vals of six hours a series of tests was made on each subject, to deter- 
mine his mental and physical condition. To eliminate the effects of 
practice, these tests were begun three days before the experiment. The 
test of the first day of experiment, before any loss of sleep had actually 
occurred, represent the normal condition of the subject. Tests were 
also made after the night’s sleep that followed the conclusion of the 
experiment. One of the writers was the first subject. The two other 
subjects were instructors in the university ; the latter were experimented 
upon at the same time. 
Some of the results are of special interest. The reaction time (for 
sound) showed a gradual increase for two of the subjects, which was 
masked in the third case by increase of practice ; at one period (differ- 
ent in the three cases) the time was considerably greater than earlier 
or later in the experiment; the mean variation was somewhat above 
the normal, but not remarkably great. The acuteness of vision, meas- 
ured by the distance at which a page of print could be distinguished 
and read, actually increased during the progress of the experiment, 
and fell off again after the ensuing sleep. The memory test of the two 
last subjects consisted in committing random series of figures; the time 
required for this memorizing fluctuated considerably, with a marked 
lengthening towards the close of the experiment. One of the subjects 
was unable to memorize the figures at all at two of the last day’s tests ; 
he found it impossible to hold the attention upon the task long enough 
to complete it. The time consumed in adding sets of figures was fairly 
constant, with two or three exceptions; it was apparently independent 
of the memory conditions. “Voluntary motor ability,” tested by the 
number of taps that could be made with the finger in five seconds, 
showed no marked alterations ; neither did the susceptibility to fatigue, 
as tested by continuing this tapping for sixty seconds. The strength of 
grip, measured on the squeeze dynamometer, fell off from 20 to 30 per 
cent. at the end of the second day, but afterwards recovered—in two 
cases fully, in the other partially. The weight of the men remained 
fairly constant, showing a slight increase towards the close of the 
period, and the variation of the pulse was within the normal range of 
daily fluctuations. 
The first subject suffered from marked visual hallucinations after the 
second night. “ The subject complained that the floor was covered with 
