126 THE WHENCE AND THE WHITHER OF MAN 



with your hand. I try hard to do so, but my eyes 

 shut for all that. I shut them unconsciously and 

 against my own will. I say, " They shut of them- 

 selves." Now, this is not true, but the explanation is 

 not difficult. These and similar actions are entirely 

 possible, although the continuity between spinal mar- 

 row and brain may have been so interrupted by some 

 accident that sensation in the reflexly active part fails 

 altogether. A bird flaps its wings after its head is 

 cut ofi', and yet the seat of consciousness and will is 

 certainly in the brain. A patient with a "broken 

 back," and paralyzed in his legs, will draw up his 

 feet if they are tickled, although he is entirely unable 

 to move them by any effort of his will and has no con- 

 sciousness of the irritation. 



The physiological action is in this case clear. The 

 vibration of the nerve caused by the tickling travels 

 from the foot to the appropriate centre in the spinal 

 marrow, and here gives rise to, or is switched off as, a 

 motor impulse travelling back to the muscles of the 

 leg, causing them to contract. In the injured patient 

 the nervous impulse cannot reach the brain, the seat 

 of consciousness, and hence this is not awakened. 

 Normally consciousness does result in a majority of 

 such cases, but only after the beginning or completion 

 of the appropriate action. Yet the movements of our 

 internal organs, intestine and heart, go on continually, 

 and in health we remain entirely unconscious of their 

 action. 



But reflex actions may be anything but simple. 

 We walk and talk, and write or play the piano with- 

 out ever thinking of a single muscle or organ. Yet we 

 had once to learn with much effort to take each step 



