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 generalizations, interesting to read, worthless to pursue. Know we then nothing leading toward a solution of the question of the proximate cause of sleep? I cannot say that, for I think we see our way to something which will unravel the phenomenon; but we must work slowly and patiently, and as men assured that, in the problem we are endeavoring to solve, we are dealing with a subject 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 temperature 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 have the representation of the same thing in the restlessness of the muscles, the half-conscious wakings, the dreams.
Suppose this idea of the change of nervous matter to be true, is there any clew to the nature of the change itself? I think there is. The change is one very closely resembling that which occurs in the solidification of water surcharged with a saline substance, or in water holding a hydrated colloid, like dialyzed silica, in trembling suspension. What is, indeed, the brain and nervous matter? It is a mass of water made sufficiently solid to be reduced into shape and form, by rather less than twenty per cent, of solid matter, consisting of albuminous substance, saline substance, fatty substance. The mechanism for the supply of blood is most delicate, membranous; the mechanism for dialysis or separation of crystalloidal from colloidal substance is perfect, and the conversion of the compound substance of brain from one condition of matter to another is, if we may judge from some changes of water charged with colloidal or fatty substances, extremely simple. I do not now venture on details respecting this peculiarly interesting question, but I venture so far as to express what I feel will one day be the accepted fact, that the matter of the wakeful brain is, on going to sleep, changed, temporarily, into a state of greater solidity; that its molecular parts cease to be moved by external ordinary
