REFLEXES 



105 



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 

 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. 

 The reflex principle is recognized in the brain as well 

 as in the cord and, in our own case, reflexes that are 

 purely regulated by the cord are not usual. 



Association Units. A diagram modified to suggest 

 the path followed by impulses when the brain figures 

 in reflex action should show more than two orders of units. 

 Thus far we have pictured the afferent element as bring- 

 ing its influence to bear directly upon the efferent. It 

 is not likely, even in the cord, that this simple relation- 

 ship is the common one. Intermediate nerve cells are 

 ordinarily concerned in the transmission. If this is 

 so, then, as a rule, more than one order of synapses 

 will lie in the path. The intermediate cells, which are 

 not clearly afferent or efferent, have been called ad- 

 justors or association units. As more and more of these 

 are introduced we have more tendency toward varia- 



