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CHAPTER XIV. 



NERVOUS POWER. 



The organs which are appropriated to the performance 

 of the various functions conducive to nutrition, are generally 

 designated the vital ors;ans^ in order to distinguish them 

 from those which are subservient to sensation, voluntary 

 motion, and the other functions of animal life. The slight- 

 est reflection on the variety and complication of actions 

 comprised under the former class of functions in the higher 

 animals, will convince us that they must be the result of 

 the combined operation of several different agents; but the 

 principal source of mechanical force required by the vital 

 organs, is still, as in all other cases, the muscular power. 

 The coats of the stomach and of the intestinal tube contain 

 a large proportion of muscular fibres, the contractions of 

 which effect the intermixture and propulsion of the con- 

 tents of these cavities, in the manner best calculated to fa- 

 vour the chemical operations to which they are to be sub- 

 jected, and to extract from them all the nourishment they 

 may contain. In like manner, all the tubular vessels, which 

 transmit fluids, are endowed w^th muscular powers adapted 

 to the performance of that office. The heart is a strong hol- 

 low muscle, with power adequate to propel the blood, with 

 immense force, through the arterial and venous systems. 

 The blood vessels, also, especially the minute, or capillary 

 arteries, besides being elastic, are likewise endowed with 

 muscular power, which contributes its share in forwarding 

 the motion of the blood, and completing its circulation. 

 The quantity of blood circulating in each part, the velocity 

 of its motion, and the heat which it evolves, are regulated 



