August 1899] A THEORY 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 {e.g. 

 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, 



