THE GENERAL FUNCTIONS OF THE NERVOUS SYSTEM 55 



FIG. 24 



(setting them in motion) and by inhibiting or checking them. From an 

 area of the cerebral cortex around or in front of the Rolandic fissure and 

 less than 7 cm. by 3 cm. in size, millions of muscle-fibers throughout the 

 opposite side of the body are directed to contract or not to contract. 

 The millions of possible combinations of these numberless muscle- 

 fibers produce in various degrees all the intricate muscular movements 

 and adjustments of civilized man. Every one of these many thousands 

 of muscle fibers should be made to contract in the proper sequence, long 

 enough and not too long, fast enough yet not too fast, and hard enough 

 and not too hard, to serve the intended purpose. We are but now, with 

 the developing knowledge of the conducting mesh which seems to make 

 up the more essential part of the neural tissue, beginning to realize 

 adequately the extreme complexity and 

 perfection of this function of the nervous 

 system. The neurone has something of a 

 new aspect. Perhaps the cerebellum has 

 more to do with actuating the movements 

 than has the Rolandic area; so, at least, 

 some investigators have recently claimed. 



Muscular movements are classified as 

 (1) deliberately voluntary ; (2) reflex; and 

 (3) "automatic" or autochthonic. Volun- 

 tary muscular movements are those made 

 with the immediate choice or will of the 

 individual. Some biologists consider these 

 the primary movements in the evolving 

 series of life. When they had been per- 

 formed often enough and generation after 

 generation long enough, they became re- 

 flex, and no longer required an act of will 

 for each performance ; they were controlled 

 then by centers situated especially in the 

 spinal cord. Those movements, however 

 (e. g., the heart-beat, peristalsis), which are of universal need and occur- 

 rence, have gone a step farther and have become "automatic," though 

 requiring actuation from the central nervous system for control. The 

 law of habit, then, has determined the status of the various muscular 

 viscera. These, or some of them, have, it is possible, learned to act per- 

 fectly as long as supplied with the needful amounts of nutriment, heat, 

 etc. Thoracic respiration is an exceptional sort of automatic series of 

 movements in which the dominating center (in the medulla oblongata) 

 is actuated by the varying quality of the blood flowing through it. In 

 this case the nerve-center is automatic rather than the muscular 

 mechanism. 



4. In controlling glandular action (that is, epithelial metabolism, which 

 usually acts to produce a secretion or an excretion) the nervous system 

 works in a manner similar to its action on the muscles. The epithelial 



The nervous net about a ciliated cell 

 from a dog's trachea. (Ploschko.) 



