1896.] Psychology. 1063 
a greasy-looking, molecular layer of rapidly moving or oscillating parti- 
cles. Often this layer was a foot above the floor and parallel with it, 
and caused the subject trouble in walking, as he would try to step up 
on it. Later the air was full of these dancing particles, which developed 
into swarms of little bodies like gnats, but colored red, purple or black. 
The subject would climb upon a chair to brush them from about the 
gas jet, or stealthily try to touch an imaginary fly on the table with his 
finger. These phenomena did not move with movements of the eye and 
appeared to be true hallucinations, centrally caused, but due no doubt 
to the long and unusual strain put upon the eyes. Meanwhile the 
subject’s sharpness of vision was not impaired. At no other time has he 
had hallucinations of sight, and they entirely disappeared after sleep.” 
Neither of the other subjects experienced these hallucinations. 
At the close of the experiment the subjects were allowed to sleep as 
long as they desired. Tests were made upon the first subject, however, 
at hourly intervals during the first night, to determine the depth of his 
sleep. He awoke naturally after ten and a half hours, and remained 
awake during the rest of the day, but slept two hours more than his 
normal amount the second night. Of the other subjects, one awoke of 
his own accord after eleven, the other after fourteen hours’ sleep ; both 
felt quite refreshed ; they required no extra sleep the next night, and 
felt no ill effects from the experiment. 
It will be noticed that the sleep made up was but asmall proportion 
of the amount lost, viz., 16, 25 and 35 per cent. in the three cases 
respectively. Two possible explanations for this are offered: either a 
greater depth of sleep may make up for a lesser duration ; or sleep is 
a relative phenomenon, and the subjects, while apparently awake, were 
in reality partially asleep at times during the experiment. The authors 
believe that both of these facts are true, and that they operated 
together in the present instance. While the subjects were not allowed 
to go tosleep for an instant, and the slightest tendency to close the eyes 
was met by active measures, still there were indications of the presence 
of dreams, in lapses of memory and occasional irrelevant remarks. “It 
must be understood,” say the writers, “that these dreams were instan- 
taneous and the subject as wide awake as he could be kept; but these 
facts reveal a cerebral condition related to sleep. This hypothesis 
alone, however, would not seen to account fully for the small proportion 
of sleep made up. And, indeed, a study of our special tests shows that 
restoration took place chiefly during the profound sleep following the 
sleep fast, and took place rapidly. That this sleep was actually more 
profound, and that the profound part of it was longer than usual, was 
shown by our experiments in depth of sleep,” on one of the subjects. 
