THE PHYSIOLOGY OF EMOTION. 283 



oxygen. When sufficient hours have been passed in sleep, slight stim- 

 uli are enough to wake him, such as a trilling noise or a light ; nay, he 

 may wake or seem to wake "of his own accord." The blood returns 

 to the brain highly oxygenized, and the brain is alive and energetic, 

 ready to expend in action the force it has accumulated in the period 

 of its rest. 



Now, be it observed, this force is accumulated by the brain in sleep, 

 when the blood-supply is at its minimum and contains the least 

 oxyo-en. Oxidation of brain, then, implies expenditure, not accumula- 

 tion of force. Stimulation of brain increases the blood-flow and 

 activity, ubi stimulus ibifluxus. But this activity cannot go on long, 

 and material for new work cannot be provided, unless the blood-flow- 

 be reduced to the sleeping-point, and the oxygen in the blood cease to 

 be consumed. 



In the creation and restoration of nerve-force, food and heat are to 

 sleep both the supplement and the complement ; without all these the 

 full energy of brain-life cannot manifest itself, except for a very limited 

 time, and each will vary in amount according as the other two are 

 supplied in greater or less quantities. To resist the cold of a northern 

 climate, the Esquimaux consumes at a meal that which would feed a 

 Hindoo for a month. If he did not, the bitter winter would bring to 

 him, no less than to the animals hybernating around him, sleep from 

 which he would not wake again. The intense desire for sleep felt by 

 persons exposed to great cold is closely akin to that produced by over- 

 whelming fatigue: the whole nerve-force is consumed in either case 

 and cannot be replaced. In those suffering from cold, the loss may be 

 met by warmth or by food ; in those worn out by fatigue, sleep alone 

 is the restorer. How completely the brain is upset by cold we may 

 learn from the striking narrative of the Arctic voyager Dr. Kane, 1 who 

 tells us, after a journey of eighty or ninety miles over the ice at a mean 

 temperature of minus 41. 2 : " We were quite delirious and had ceased 

 to entertain a sane apprehension of the circumstances about us." 

 " Our strength failed us, and we began to lose our self-control. . . 

 We fell half-sleeping on the snow. I could not prevent it. Strange 

 to say, it refreshed us. I ventured upon the experiment myself, mak- 

 ing Riley wake me at the end of three minutes ; and I felt so much 

 benefited by it that I timed the men in the same way. They sat on 

 the runners of the sledge, fell asleep instantly, and were forced to 

 wakefulness when their three minutes were out." 



The fact, that pleasure and pain depend on fatigue and the con- 

 sumption of this nerve-force, is closely connected with two other 

 phenomena : one, that the stimulation of any nerve-centre, if repeated, 

 loses somewhat of its effect ; the other, that the same stimulus, if pro- 

 longed or intensified, may cause every variety of feeling from 



1 "Arctic Explorations," L, 198. 



