THE NERVOUS SYSTEM 87 



brain of the developing child is a veritable ta- 

 bula rasa on which environment through the 

 sense organs writes the story of life. Innate 

 ideas there are none. The uninvaded mind is 

 hke a machine in readiness for operation, but 

 awaiting the arrival of that first flow of power 

 to initiate its processes. Like the lung, it 

 stands in perfect physical readiness for action ; 

 at birth the stimulus for the first inspiration 

 occurs and the respiratory mechanism that is 

 to run till the end of life is started. 



In stating briefly the modern conception 

 concemingr the source of the contents of the 

 mind, I have put the matter almost in the 

 words of Locke, but the present aspect of this 

 subject is not based upon philosophical spec- 

 ulation ; it is grounded upon observed fact. We 

 know that when we sleep we revert to a con- 

 dition of relatively simple reflexes and that 

 intelligence vanishes in the assumption of the 

 unconscious state. To induce this condition 

 under normal circumstances, we check as far 

 as possible all sensory inflow by lying down 

 in a darkened, quiet situation. The impulses 

 from the organs of touch, equilibrium, and 

 especially of hearing and sight, having been 

 reduced to a minimum, the activity of the 



