ON SLEEP 



503 



Sleep is thus an absolutely physiological condition, and 

 its incidence is due to the operation of physiological 

 factors, these factors being confined, in their range of 



7 O O 



incidence and influence, to the specific histological or 

 neuronal elements of the systemic nervous system, and 

 the dynamic activities of that system, to the end that 

 cerebration in its full and true sense should, or might, be 

 maintained at its highest and most sustained and effective 

 pitch or level ; in other words, to borrow a " working " 

 simile, it constitutes the period of rest for the neuro-systemic 

 manufactory or industry, to let off steam, clean and oil 

 machinery, remove debris, re-stock with fresh raw 

 materials, and again get up steam. It, therefore, comes 

 between the ego, or central immaterial essentiality or 

 essence, and the sympathetic nervature or vital materio- 

 dynamic essentiality, with a range of temporarily function- 

 less matefio-dynamic neuro-muscular structures, which 

 effectually bar united, active, and co-ordinated cerebration, 

 including sensory and motor activities, and intelligence in 

 all its phases, excepting during incomplete incidence and 

 dreams in all their varieties. 



We are warranted, therefore, in inferring that total 

 cerebro-spinal temporary paralysis or inhibition, on which 

 sleep is dependent for its induction and continuance, 

 coincides with, and is due to, a solution of continuity 

 or contiguity, as the case may be, of the nerve cell 

 processes of the purely psychic or mental higher systemic, 

 and the cerebro-spinal neurons generally, and ceases when 

 that continuity or contiguity is, or becomes, re-established. 

 It is rhythmic in occurrence, coinciding or synchronising, 

 in the human species generally, with the " day's decline," 

 or onset of darkness, and terminating with the dawn, or 

 from when the stimuli of light and sound are withdrawn, 

 and the " silence of nature " is established, the sensorium 

 then losing its receptive and responsive, or sensory and 

 motor, powers, until they are renewed ; in the lower 

 animal and vegetable worlds, however, a greater variety 

 in the incidence of sleep takes place to a great extent, 

 apparently due to the acquirement of habit and the 

 requirements of environment. 



The length of its duration is as various as the 



