COORDINATION 



83 



entirely confined to the brain or cord and group together 

 those efferent cells which by working together produce a 

 coordinated action. 



The organization of the nervous system is, in fact, much 

 like that of a large manufacturing establishment. The nerve 

 cells which send axons to the muscles, glands, blood vessels, 

 etc. may be compared with the operatives, each with his 

 special task to perform ; over these are foremen, or " bosses," 

 from whom they take their orders or, in physiological 

 language, who stimulate 

 them to do their work 

 and who would corre- 

 spond to cells like a in 

 Fig. 48. The foremen in 

 turn receive orders, now 

 from one department of 

 the establishment, now 

 from another, as the work 

 of their operatives is 

 needed in making one or 

 the other of the products 

 offered for sale. So the 

 master neurones receive 

 stimuli from the brain or from afferent nerves, as the needs 

 or the desires of the organism as a whole require their 

 activity. The comparison is instructive and may easily be 

 carried out in greater detail by the student himself. 



14. The coordination of two or more actions to achieve a 

 definite end. These conceptions will become more definite if 

 we study the nervous mechanisms represented in Fig. 49, 

 which represents the combination of the wink with different 

 physiological actions, according to the nature of the con- 

 ditions which call it forth. Let us consider the two reflex 

 winks already referred to, that from the cornea and that from 

 the retina. The wink from the cornea is for the purpose of 



FIG. 48. The master neurone 



