( } >i tlic St it-iit ijic Study of Human Xaturc. 457 



chain of nerve centres, and that impressions reaching it 

 from the surface through the sensory nerves may he im- 

 mediately reflected hack, through tlie motor nerves, upon 

 the muscles, thus producing bodily movements, without the 

 brain being at all involved. This is termed reflex action. 

 Thus, if the foot of a sleeper be tickled, it will be jerked 

 away that is, the impression from the skin is conveyed to 

 the spinal centre, and an impulse is immediately reflected 

 back, which contracts the proper muscles of the limbs, and 

 the foot is withdrawn. The most perfect example of it, 

 however, is where stimulus at the surface produces move- 

 ments of the limbs after division of the cord from the head, 

 and therefore in total unconsciousness. The discovery of 

 reflex action was the first step in the systematic elucidation 

 of the spontaneous movements, or what is known as the 

 automatic system in animal mechanisms. 



But reflex action has another aspect. When an impres- 

 sion passes upward along the cord to the nervous masses 

 at the base of the brain, it first flashes into consciousness 

 and becomes a sensation. Reflex effects now take place, 

 in which sensation and consciousness are implicated. Wink- 

 ing, sneezing, coughing, swallowing, are examples : we are 

 conscious of the actions, but they are not the results of 

 volition. The will may, indeed, exert a partial control 

 over them, but they are usually of an automatic character. 

 Thus far, the part of the nervous mechanism called into 

 action is the spinal system, and the ganglionic masses at 

 the base of the brain known as the sensorium. This appa- 

 ratus is not peculiar to man ; he shares it with the entire 

 vertebrate series, and it is regarded as the source of all 

 purely instinctive actions. 



The establishment of these fundamental facts in refer- 

 ence to the working of the mental mechanism of our nature 

 the definite separation of a large part of its actions from 

 that higher sphere of intellection and volition to which 



