INTRODUCTION TO 



THE COMPARATIVE PHYSIOLOGY 

 OF THE BRAIN 



CHAPTER I 



SOME FUNDAMENTAL FACTS AND CONCEPTIONS 

 CONCERNING THE COMPARATIVE PHYSIO- 

 LOGY OF THE CENTRAL NERVOUS SYSTEM 



i. The understanding of complicated phenomena 

 depends upon an analysis by which they are resolved 

 into their simple elementary components. If we ask 

 what the elementary components are in the physio- 

 logy of the central nervous system, our attention is 

 directed to a class of processes which are called re- 

 flexes. A reflex is a reaction which is caused by an 

 external stimulus, and which results in a coordinated 

 movement, the closing of the eyelid, for example, 

 when the conjunctiva is touched by a foreign body, 

 or the narrowing of the pupil under the influence of 

 light. In each of these cases, changes in the sensory 



