AuGusT 1899] A PAHRORY OF SLEEP 135 
light and heat, endowed with a certain degree of intensity, produce an 
abundance of sap in the cells which increases the turgescence: it can 
then resist the action of the opposite factor.” In short, this is but a 
mechanical effect of the delay of the nutritive currents coming up the 
leaves. 
Dreams. 
These vary both in essence and degree according to the state of 
the dreamer’s circulation. Some hygienic exercise or the repetition of 
a lesson may probably cause certain neurons to go on moving during 
sleep. But when they have worked too actively in the course of the 
day they are liable to be utterly drained and exhausted when night 
comes, and when such is the case there may be dreaming of the facts 
that brought their fatigue about. An assiduous exercise of the 
neurons may facilitate their continuous development and action (eg. 
in the student dreaming about his examinations again and again). 
Contrariwise, the absence of new impressions, or a limited exercise 
during the day, will allow the uniform rest of all the neurons and a 
thorough absence of nightmare (husbandmen). 
Fixed ideas lead to madness, perhaps on account of an atrophy of 
the inactive parts, some limited congestions, hypertrophies, etc. This 
is no business of mine, but I must state that the possibility of the 
functions of some cerebral centres being accomplished independently 
is made manifest during sleep. This means that certain neurons 
become associated in an abnormal way, extending themselves too much, 
and that diseases of mind, disordered neuroplasmic vibrations, are not 
inhibited by the more powerful vibrations of sound judgment, this 
being then peacefully slumbering. 
Causes of Sleep. 
Theories on this subject are by no means wanting, but they con- 
cern man only; they are not capable of general application, and leave 
the innermost mechanism of the phenomena unexplained. I admit, if 
necessary, the action of poisons and that of the secretions of the 
organism accumulated during the day, but chloroform and hypnotism 
work in the same manner. Whether the brain be congested or 
whether it be anaemic, its functions are deeply modified on account of 
the delay of the currents. Moreover, the lowest animals (Protozoa) 
sleep and wake in accordance with the conditions of their activity. 
I believe, therefore, that sleep originates, either in man or infusorian, 
in a delay or slowing of the protoplasmic or neuroplasmic currents, 
due to refrigeration, lack of nutritive fluids, congestion or anaemia. 
Everything grows wearied. Everything bores and is bored. Both 
Biitschli’s foam and my protoplasmic mass made by synthesis, 
cease from visible movement after a certain period of activity. Briefly, 
