104 



HUMAN PHYSIOLOGY 



to cough or sneeze when we would much rather not. 

 Yet there are reactions which we are inclined to call 

 reflex which nevertheless depend much upon the color- 

 ing of our consciousness. Take, for example, the water- 

 ing of the mouth at the sight of delicious food or 

 of a lemon. Here is a response which is determined by 

 external stimuli but which would not take place in an 

 unconscious nor even in an inattentive subject. The 

 secretion of gastric juice normally accompanies the 

 taking of food but only when there is an element of 



FIG. 24. This differs from the second diagram in Fig. 23 in the fol- 

 lowing respect. The afferent fiber does not connect directly with the 

 motor cells but with intermediate or association neurons whic~h extend 

 the effect of the original impulse to groups of efferent elements. 



pleasure. The term psycho-reflex is applied to such 

 adaptive changes as these. 



The Position of Reflex Arcs. Our conventional 

 diagrams usually represent segments of the spinal cord 

 as containing the synapses through which reflexes are 

 brought about. We are entirely warranted in this 

 representation, for certain reflexes can be mediated 

 by the spinal cord when it' has been separated from the 

 brain. Still, it would be wrong to leave the impression 

 that the cord, in the higher animals, plays the leading 

 part in coordinating incoming with outgoing impulses. 



