THE CONCEPTUAL WORLD 5 



parts of the body. Within the body itself certain 

 tracts of protoplasm are differentiated so that they 

 can conduct molecular disturbances set up in the 

 receptor organs in the integument better than can the 

 general protoplasm ; these are the nerves. Other 

 parts are modified so that they can contract or secrete 

 the more easily ; these are the muscles and glands. 

 The conception of a reflex action, as it is usually stated 

 in books on physiology, therefore includes this idea 

 of the differentiation of the tissues, but all the pro- 

 cesses that are included in the typical reflex are pro- 

 cesses which can be carried on by undifferentiated 

 protoplasm. 



It is also a schematic description that assumes a 

 simplicity that does not really exist. As a rule a 

 reflex is initiated by the stimulation of more than one 

 receptor organ, and the impulses initiated may thus 

 reach the central nervous system by more than one 

 path. There is no simple shunting of the afferent 

 impulse from the cell in which it terminates into 

 another nerve, when it becomes an efferent impulse ; 

 but, instead of this, the impulse may " zigzag " through 

 a maze of paths in the brain or spinal cord connecting 

 together afferent and efferent nerves and ganglia. 

 Further, the final part of the reflex, the muscular 

 contraction, is far from being a simple thing, for 

 usually a series of muscles are stimulated to contract, 

 each of them at the right time and with the right 

 amount of force, and every contraction of a muscle 

 is accompanied by the relaxation of the antagonistic 

 muscle. There are muscles which open the eyelids and 

 others which close them, and the cerebral impulse 

 which causes the levators to contract at the same time 

 causes the depressors to relax. 



It is quite necessary to remember that the simple 



