290 



SCIENCE 



[N. 8. Vol. XXXVIII. No. 974 



sciousness would have steadily changed 

 until it culminated in the permanent un- 

 consciousness of death. An examination of 

 the brain cells of these animals showed 

 physical changes identical with those pro- 

 duced by exhaustion from other causes, 

 such as prolonged physical exertion or 

 emotional strain. After 100 hours of wake- 

 fulness the rabbits were allowed a long 

 period of sleep. All the brain cells were 

 restored except those that had been in a 

 state of complete exhaustion. A single 

 seance of sleep served to restore some of the 

 cells, but those which had undergone ex- 

 treme changes required very prolonged 

 rest. These experiments give us a definite 

 physical basis for explaining the cost to 

 the body mechanism of maintaining the 

 conscious state. We have stated that the 

 brain cell changes produced by prolonged 

 consciousness are identical with those pro- 

 duced by physical exertion and by emo- 

 tional strain. Rest, then, and especially 

 sleep, is needed to restore the physical state 

 of the brain cells which have been im- 

 paired, and as the brain cells constitute the 

 central battery of the body mechanism, 

 their restoration is essential for the main- 

 tenance of normal vitality. 



In ordinary parlance, by consciousness 

 we mean the activity of that part of the 

 brain in which associative memory resides, 

 but while associative memory is suspended 

 the activities of the brain as a whole are 

 by no means suspended; the respiratory 

 and circulatory centers are active, as are 

 those centers which maintain muscular 

 tone. This is shown by the muscular re- 

 sponse to external stimuli made by the nor- 

 mal person in sleep ; by the occasional acti- 

 vation of motor patterns which may break 

 through into consciousness causing dreams ; 

 and finally by the responses of the motor 

 mechanism made to the injuring stimuli 



of an operation on a patient under inhala- 

 tion anesthesia only. 



Direct proof of the mechanistic action of 

 many of life's phenomena is lacking, but 

 the proof is definite and final of the part 

 that the brain cells play in maintaining 

 consciousness; of the fact that the degree 

 of consciousness and mental efficiency de- 

 pends upon the physical state of the brain 

 cells; and finally that efficiency may be 

 restored by sleep, provided that exhaus- 

 tion of the cells has not progressed too far. 

 In this greatest phenomenon of life, then, 

 the mechanistic theory is in harmony with 

 the facts. 



Perhaps no more convincing proof of 

 our thesis that the body is a mechanism de- 

 veloped and adapted to its purposes by 

 environment can be secured than by a 

 study of that most constant manifestation 

 of consciousness — pain. 



Like the other phenomena of life, pain 

 was undoubtedly evolved for a particular 

 purpose — ^surely for the good of the indi- 

 vidual. Like fear and worry, it frequently 

 is injurious. What then may be its pur- 

 pose? 



We postulate that pain is a result of con- 

 tact ceptor stimulation for the purpose of 

 securing protective muscular activity. 

 This postulate applies to all kinds of pain, 

 whatever their cause — whether physical in- 

 jury, pyogenic infection, the obstruction 

 of hollow viscera, childbirth, etc. 



All forms of pain are associated with 

 muscular action, and as in every other 

 stimulation of the ceptors, each kind of 

 pain is specific to the causative stimuli. 

 The child puts his hand in the fire ; physi- 

 cal injury pain results and the appropriate 

 muscular response is elicited. If pressure 

 is prolonged on some parts of the body, 

 anemia of the parts may result, with a cor- 

 responding discomfort or pain, requiring 

 muscular action for relief. When the rays 



