316 ADVANCED PHYSIOLOGY 



It is not difficult to cite instances of brain reflexes. If a 

 sudden light flashes in front of the eyes, or if another person 

 shakes a handkerchief or other solid object toward the face, 

 one shuts the eyes instantly. Now a person does not stop 

 to think whether or not he will shut his eyes under these cir- 

 cumstances. They are closed before he realizes it and he 

 himself is opening them carefully, lest the danger is not yet 

 passed. Yet all the nerves controlling the eye muscles come 

 directly from the brain, and the centers from which they 

 arise have acted without the person's conscious volition. 

 Ordinary winking is carried on unconsciously, as we know. 

 The surface of the eye becomes slightly dry, and this condi- 

 tion irritates it. Messages go to the centers controlling the 

 winking muscles, they act and the eyes wink, but the whole 

 process takes place without one's being aware of it. In tak- 

 ing food into the mouth, the movements of the tongue and 

 jaw, while under one's control, nevertheless occur without 

 conscious thought about it. One does not say to himself, 

 "I will now shut my mouth," and afterwards, " I will now 

 open my mouth." These are only two of the innumerable 

 instances of unconscious action on the part of brain 

 centers. 



In the above illustrations of reflex actions we have con- 

 fined ourselves to visible movements. There are innumerable 

 muscular and glandular activities in the body of which one 

 has absolutely no intimation, which also come under this 

 head; e. g. respiratory movements and the movements of the 

 stomach and intestinal walls. Before any of these occur, 

 messages first go from the organ concerned to the central 

 nervous system. For example, when the stomach is empty 

 it lies perfectly passive, but if food is swallowed, the ends of 

 nerves in the stomach are stimulated. They carry the mes- 

 sage to some center in the gray matter of the cord or brain, or 

 both, and immediately impulses are sent out over motor nerves 

 to the muscles of the stomach walls, which then begin their 



