588 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
- Or is our consciousness discontinued? If it be not continuous, how 
can we account for that deep feeling that we have of the unity and 
continuity of our personality ? 
Moreover, how do we distinguish the dream from the reality? 
Descartes says: 
How many times at night have I thought that I was in a certain room, that I was 
clothed, that I was near the fireplace, although I was undressed and in my bed! It 
is plain to me at this moment that it is not at all with sleepy eyes that I behold this 
paper; that this head that I nod is not at all drowsy; that it is with design and delib- 
erate purpose that I extend this hand and feel of it. What happens to me in my sleep 
is not near so clear and distinct as this. 
We certainly distinguish far more clearly the incidents of our 
daily life than those of our dreams. Yet, after all, who has not asked 
himself on waking up whether these thoughts were visions or the 
reality? And how can he be sure which is correct? This explains the 
perplexity of Pascal when he says: 
Who knows whether that other part of life when we think we are awake is but 
another kind of sleep, a trifle different from the first, to which we are aroused when 
we think we are asleep? 
These two conceptions of a continuous personality and of the reality 
are subjects of psychological studies relative to sleep. Not only do 
psychologists observe these in respect to themselves but their vari- 
ations in other persons. And they have demonstrated some curious 
phenomena. Though most men have a distinctive and strong person- 
ality, there are those in whom personality is disorganized, and some 
have come to have two absolutely independent personalities, as the 
hysterical individuals observed by MacNish, Azam, and others. 
Though the majority of men clearly distinguish the genuine from 
dreams, it is equally true that some can not make this distinction and 
take their dreams for realities and realities for dreams. Disorders of 
the personality and the perception of the reality are, however, patho- 
logical conditions and their study is altogether more within the 
domain of the physician than of the psychologist. The physician 
devotes himself to numerous problems pertaining to sleep. Aside 
from the hygiene of normal sleep which is within his jurisdiction, he 
must also consider its disturbances, such as hysteria and various con- 
ditions more or less comparable to sleep, as hypnotism, lethargy, 
anesthesia, coma, sleeping sickness, and the like. 
Hysteria is an illness that most disturbs sleep. Besides the con- 
ditions of disorganization of the personality and the loss of percep- 
tion of the reality of which I have spoken, hysteria presents other 
disorders, either provoked, as in hypnotism, or involuntary, as in 
lethargy. A discussion of these phenomena would be very interest- 
ing, but it would take too long a time. 
