4 i8 THE POPULAR SCIENCE MONTHLY. 



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, worth- 

 less 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 phenome- 

 non ; 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 sub- 

 ject of more than ordinary importance. I will try to point out the di- 

 rection 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 ne- 

 cessary 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 ner- 

 vous 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 rest- 

 lessness 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 suspen- 

 sion. 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 albu- 

 minous 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 in- 

 teresting 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 solid- 

 ity ; that its molecular parts cease to be moved by external ordinarv 



