ON SLEEP. 
65 
correct. The theory that sleep is caused by withdrawal of 
blood from the brain by contraction of its arterial vessels, is 
disproved by many considerations. It presupposes that at the 
time when the cerebro-spinal nervous system is most wearied 
the organic system is most active ; and it assumes that the great 
volume of blood which circulates through the brain can be cut 
off without evidence of increased volume of blood and tension of 
vessel in other parts of the body, a supposition directly negatived 
by the actual experiment of cutting off the blood from the brain. 
There is another potent objection applicable to both 
theories. When sleep is artificially induced, either by subject- 
ing the brain to pressure of blood or to exhaustion of blood, 
the sleep is of such a kind that the sleeper cannot be roused 
until the influence at work to produce the sleep is removed. 
But in natural sleep the sleeper can always be roused by motion 
or vibration. We call to a person supposed to be sleeping 
naturally, or we shake him, and if we cannot rouse him we know 
there is danger ; but how could these simple acts remove 
pressure from the brain, or relax the contracted vessels feeding 
the brain ? 
These two theories set aside, the others I have named need 
not trouble us ; they are mere generalisations, interesting to 
read, worthless to pursue. Know we then nothing leading to- 
wards a solution of the question of the proximate cause of 
sleep ? I cannot say that, for I think we see our way to some- 
thing which will unravel the phenomenon ; but we must work 
slowly and patiently, and as men assured that in the pro- 
blem we are endeavouring to solve, we are dealing with a sub- 
ject of more than ordinary importance. I will try to point out 
the direction of research. 
I find that to induce sleep it is not necessary to produce 
extreme changes of brain matter. In applying cold, for 
example, it is not necessary to make the brain substance solid 
in order to induce stupor, but simply to bring down its tem- 
perature ten or twelve degrees. I find also that very slight 
direct vibrations, concussions, will induce stupor ; and I find 
that in animals of different kinds the profoundness of sleep is 
greater in proportion as the size of the brain is larger. From 
these and other facts I infer that the phenomenon of natural 
sleep is due to a molecular change in the nervous structure 
itself of the cerebro-spinal system, and that in 'perfect sleep the 
whole of the nervous structure is involved in the change — the 
brain, the cord, the nerves ; while in imperfect sleep only parts 
of this nervous matter are influenced. This is in accord with 
facts, for I can by cold put to sleep special parts of the nervous 
mass without putting other parts to sleep. In bad sleep we 
VOL. X. — NO. XXXVIII. E 
