NERVOUS POWER. 321 



shown that the due performance of the vital func- 

 tions of digestion, of circulation, and of secretion, 

 requires the presence of an agency, derived from 

 different parts of the brain and spinal cord, and 

 regulating the order and combinations of the actions 

 of the organs which are to perform those functions. 

 The same influence, for example, which increases 

 the power of secretion in any particular gland, is 

 found to increase, at the same time, the action of 

 those blood-vessels which supply that gland with 

 the materials for secretion ; and conversely, the 

 increased action of the blood-vessels is accompa- 

 nied by an increased activity of the secreting 

 organ. Experience also shows that when the in- 

 fluence of the brain and spinal cord is intercepted, 

 although the afilux of blood may, for a time, con- 

 tinue, yet the secretion ceases, and all the functions 

 dependent upon secretion, such as digestion, cease 

 likewise. Thus the nervous power combines toge- 

 ther different operations, adjusts their respective 

 degrees, and regulates their succession, so as to 

 ensure that perfect harmony which is essential to 

 the attainment of the objects of the vital functions ; 

 and thus, not only the muscular power which re- 

 sides in the vital organs, but also the organic affini- 

 ties which produce secretion, and all those unknown 

 causes which effect the nutrition, developement, 

 and growth of each part, are placed under the con- 

 trol of the nervous power.* 



* As the functions of plants are sufficiently simple to admit of 

 being conducted without the aid of muscular power, still less do they 

 require the assistance of the nervous energy ; both of which proper- 

 ties are the peculiar attributes of animal vitality. We accordingly 

 find no traces either of nervous or of muscular fibres in any of the 

 vegetable structures. 



VOL. II. Y 



