102 liTJxMAN MIYSIOLOGY 



of our situation. Yet we must admit that external 

 forces guide us in the performance of many acts which 

 we confidently call voluntary. When we walk, our 

 muscular contractions are modified every moment by 

 stimuli from many sources. Some of these we shall 

 have to analyze a little later. A child who is painfully 

 copying a word from the blackboard is really making 

 movements which are shaped by the visual stimuli he 

 receives. But we feel instinctively that it is a long re- 

 move from the simple reflex to an instance like this. The 

 question that cannot be put aside is: What is our will 

 and how far is it a positive force in shaping our conduct? 

 The physiologist defers to the philosopher at this point, 

 but as a human being he knows that one's conscience and 

 one's fellow men applaud a faith in one's moral freedom. 



If an act is not to be classed as reflex, in any degree 

 whatever, it must be one in which the origin is clearly 

 central and unaided by any afferent impulses. We 

 are disposed to think that this condition is realized in 

 those actions which we call voluntary; yet from another 

 point of view these can be regarded as delayed reflexes. 

 They are determined by external stimuli some of which 

 may have been brought to bear a long time before the 

 occasion. A man somewhat suddenly decides to walk 

 up a hill to enjoy a prospect which he has seen the 

 previous year. We describe the act as voluntary but 

 at least one of the factors concerned in causing it is 

 the impression made upon his nervous system at the 

 time of his earlier visit. So the discussion of reflexes 

 leads not only to the problems of habit but to those of 

 memory. This subject will be more advantageously 

 considered in connection with the cerebrum. 



Examples of Reflex Action. We have spent a good 

 deal of time in treating the topic in general terms. 

 Let us now turn to some specific illustrations. What 

 are some of the reflexes exhibited by a baby and how 

 do they make for its welfare? One thinks imme- 

 diately of the sucking reflex. The infant sucks vigor- 



