ON SLEEP. 
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tant changes of nutrition are in progress ; the body is reno- 
vating, and if young is actually growing ; if the body be 
properly covered, the animal heat is being conserved and 
laid up for expenditure during the waking hours that are to 
follow ; the respiration is reduced, the inspirations being 
lessened in the proportion of six to seven as compared with the 
number made when the body is awake ; the action of the 
heart is reduced ; the voluntary muscles, relieved of all fatigue 
and with the extensors more relaxed than the flexors, are under- 
going repair of structure and recruiting their excitability ; and 
the voluntary nervous system, dead for the time to the exter- 
nal vibration, or as the older men called it “ stimulus ” from 
without, is also undergoing rest and repair, so that when it 
comes again into work it may receive better the impressions 
it may have to gather up, and influence more effectively the 
muscles it may be called upon to animate, direct, control. 
Thirdly, although in the organism during sleep there 
is suspension of muscular and nervous power, there is not 
universal suspension ; a narrow, but at the same time safe, line 
of distinction separates the sleep of life from the sleep of 
death. The heart is a muscle, but it does not sleep, and 
the lungs are worked by muscles, and these do not sleep ; and 
the viscera which triturate and digest food are moved by 
muscles, and these do not sleep ; and the glands have an 
arrangement for the constant separation of fluids, and the 
glands do not sleep ; and all these parts have certain nerves, 
which do not sleep. These all rest, but they do not cease 
their functions. Why is it so ? 
The reason is that the body is divided into two systems as 
regards motion. For every act of the body we have a system 
of organs under the influence of the will, the voluntary, and 
another system independent of the will, the involuntary. 
The muscles which propel the body and are concerned in all 
acts we essay to perform, are voluntary ; the muscles, such as 
the heart and the stomach, which w T e cannot control, are 
involuntary. Added to these are muscles which, though com- 
monly acting involuntarily, are capable of being moved by 
the will : the muscles which move the lungs are of this order* 
for we can if we wish suspend their action for a short time 
or quicken it ; these muscles we call semi-voluntary. In 
sleep, then, the voluntary muscles sleep, and the nervous 
organs which stimulate the voluntary muscles sleep ; but the 
involuntary and the semi-voluntary muscles and their nerves 
merely rest : they do not veritably sleep. 
This arrangement will be seen, at once, to be a necessity, for 
upon the involuntary acts the body relies for the continuance 
of life. In disease the voluntary muscles may be paralysed, the 
