INTRODUCTION. 13 



production of liquids ; while that of nutrition is more especially applied 

 to the formation and deposition of the matter necessary to the growth 

 and conservation of the solids. 



The composition of every solid organ, and of every fluid, is precisely such 

 as fits it for the part it is to play, and it preserves it as long as health 

 remains, because the blood renews it as fast as it becomes changed. 



O 



The blood itself by this continued contribution is changed every 

 moment, but is restored by digestion, which renews its matter ; by 

 respiration, which delivers it from superfluous carbon and hydrogen ; 

 and by perspiration and various other excretions, that relieve it from 

 other superabundant principles. 



These perpetual changes of chemical composition form a part of the 

 vital vortex, not less essential than the visible movements and those of 

 translation. The object of the latter is, in fact, but to produce the 

 former. 



OP THE FORCES WHICH ACT IN THE ANIMAL BODY. 



The muscular fibre is not only the organ of voluntary motion, for 

 we have just seen that it is also the most powerful of the agents 

 employed by nature to produce those transmutations so necessary to 

 vegetative life. Thus the fibres of the intestines produce the peristaltic 

 motion, which causes the alimentary matter therein contained to pass 

 through them ; the fibres of the heart and arteries are the agents of 

 the circulation, and through it of all the secretions, &c. 



Volition contracts the fibre through the medium of the nerve ; and 

 the involuntary fibres, such as those we have mentioned, being also 

 animated by them, it is probable that these nerves are the cause of their 

 contraction. 



All contraction, and, generally speaking, every change of dimension 

 in nature, is produced by a change of chemical composition, though it 

 consists merely in the flowing or ebbing of an imponderable fluid, such 

 as caloric ; thus also are produced the most violent movements known 

 upon earth, explosions, &c. 



There is, consequently, good reason to suppose that the nerve acts 

 upon the fibre through the medium of an imponderable fluid, and the 

 more so, as it is proved that this action is not mechanical. 



The medullary matter of the whole nervous system is homogeneous, 

 and must be able to exercise its peculiar functions wherever it is found; 

 all its ramifications are abundantly supplied with blood vessels. 



