2 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



nerve-endings are produced which bring about a 

 change of condition in the nerves. This change 

 travels to the central nervous system, passes from 

 there to the motor nerves, and terminates in the 

 muscle-fibres, producing there a contraction. This 

 passage from the stimulated part to the central 

 nervous system, and back again to the peripheral 

 muscles, is called a reflex. There has been a growing 

 tendency in physiology to make reflexes the basis of 

 the analysis of the functions of the central nervous 

 system, consequently much importance has been at- 

 tached to the underlying processes and the necessary 

 mechanisms. 



The name reflex suggests a comparison between 

 the spinal cord and a mirror. Sensory stimuli were 

 supposed to be reflected from the spinal cord to the 

 muscles ; destruction of the spinal cord would, ac- 

 cording to this, make the reflex impossible, just as 

 the breaking of the mirror prevents the reflection of 

 light. This comparison, however, of the reflex pro- 

 cess in the central nervous system with the reflection 

 of light has, long since, become meaningless, and at 

 present few physiologists in using the term reflex 

 think of its original significance. Instead of this, 

 another feature in the conception of the term reflex 

 has gained prominence, namely, the purposeful char- 

 acter of many reflex movements. The closing of the 

 eyelid and the narrowing of the pupil are eminently 

 purposeful, for the cornea is protected from hurtful 

 contact with foreign bodies, and the retina from the 



