814 Dynamic Theory. 



ness is aroused. Whenever there is consciousness, it implies work on 

 the part of the brain as to the subjects to which the consciousness re- 

 lates. For we are not conscious of many things at a time. There may 

 also be a certain degree of brain activity without arousing conscious- 

 ness. Brain work, including consciousness, is, like muscle work, done 

 at the expense of its own tissue, which is in part disrupted and wasted 

 in the operation. ( See page 497. ) When this waste has gone on to a 

 certain extent, the functional activity of the cells wasted necessarily 

 decreases, attention ends, and the blood supply to them is automatically 

 diminished. Repair begins as soon as waste begins, and it continues 

 after work and waste have ceased. This is a process the reverse of 

 waste. From the same blood from which the elements of motion were 

 derived, the cells, by the chemical affinity of their now to some extent 

 nascent elements, take up the equivalents of the chemical molecules they 

 have lost. Consciousness is a form of work; consequently, when it 

 disappears it is an indication that work has ceased to a certain extent, if 

 not entirely. We know that a certain amount of brain work may go on 

 in unconsciousness, but ordinarily the most of the brain work ceases 

 with the disappearance of consciousness, because the supply of blood 

 necessary for its production has by that time become too limited. 



The attention ends when, by reason of the exhaustion of the brain 

 cells, the incoming ordinary stimulus is unable any longer to produce 

 their erection. They are, however, in the general conditions of health- 

 ful sleep, subject to erection by an extraordinary stimulation. But the 

 exhaustion may become too great for any but the most violent stimuli. 

 People upon whom torture is being inflicted, will often sleep in the in- 

 tervals of its torments. This is told of Indians at the stake, and of 

 Christian martyrs on the rack. It is also true of soldiers in the din of 

 battle. There are different sorts of predisposing causes to sleep, all of 

 which depend, however, upon the same principle of withdrawing the 

 blood supply from the brain cells. If the stomach be overloaded, the 

 muscular and chemical work put upon it is excessive, and an increased 

 supply of blood is directed to it, and to the related organs concerned in di- 

 gestion. This withdraws it from the brain and induces drowsiness or 

 sleep. Fatiguing work by the muscles operates in a similar way. The 

 hum of a mill, the gentle, monotonous beating of waves upon a beach, 

 the droning of a dull reader, or the perusal of a dull book, produce the 

 same result. In this sort of cases the monotonous succession of im- 

 pressions made upon the sensory ganglia, does not lead to the stimula- 

 tion of cerebral cells in the formation of ideas, because the attention is 

 held to the sensory impression by the continued repetition of the sen- 

 sory stimulus upon the cells of the sensory ganglia. So the accession of 

 blood to the idea-forming cells is diminished, and they may all sink to 



