68 "hi.icup anjj dueams." 



After a certain number of y(!iir.s tlio cerebral cortex be- 

 comes more automatic and less dependent on stimuli from 

 without. It lives on past perceptions; and just as wa,lkinf,' 

 at first requires every movement to be carefully plainuid, 

 yet after a time biicoraes an unconscious action, so the 

 nnmborless impulses ca-rried tlirough many years to the 

 cortex, arc stored up by it as experience and memory. 

 I think, therefore, that what we call wakcfiilncKS is, in a 

 groat measure, the result of the action of our sui'ronnd- 

 ings on our easily stimulated nerves; and other things 

 being equal, the more excitement and activity ii,nd fi:ic;tioM 

 that go on around us, the more vitality will be called forth. 



This theory does not, however, altogethei' explain matters. 

 We are the servants of habit a,nd the slaves of instinct. It 

 is the l!i,w of the animal world that at some period during 

 the twenty-four hours we should sleep, and we inherit this 

 habit as we do others. We sleep because it is our instinct to 

 do so, and this instinct cannot be broken through. It is a 

 part of that rhythm which runs through nature. We have 

 accumulated it during thousands of years ; but even during 

 the comparatively short time that man has set apai"t one 

 day in the week for rest, some people have already ac(iuirud 

 a " seventh day's resting " instinct, and can tell without 

 an almanack when Sunday morning comes round by the 

 indifference they feel to exertion; and there is no doubt, 

 I suppose, tliat some domestic animals experience this to 

 a certain degree. This, then, is another reason of our 

 nocturnal i-ost. 



Now it has boon stated that the immediate cause of sleep 

 IS a bloodless condition of the l)rain; this, indeed, is tlio 

 commonly received theory. With whom it originated J 

 do not know, but Dr. Hammond and Mr. Darham proved 

 pretty conclusively, from experiments on animals, that the 



