COMPLEX APPARATUS FOR NUTRITION. 109 



which these functions are conducted in the seve- 

 ral tribes of animals will be described hereafter. 

 It will be sufficient for our present purpose to 

 state, by way of completing the outline of this 

 class of functions, that, like the returning sap 

 of plants, the blood is made to undergo farther 

 modifications in the minute vessels through 

 which it circulates ; new arrangements of its 

 elements take place during its passage through 

 the subtle organization of the glands, which no 

 microscope has yet unravelled : new products 

 are here formed, and new properties acquired, 

 adapted to the respective purposes which they 

 are to serve in the animal economy. The whole 

 is one vast Laboratory, where mechanism is sub- 

 servient to Chemistry, where Chemistry is the 

 agent of the higher powers of Vitality, and where 

 these powers themselves minister to the more 

 exalted faculties of Sensation and of Intellect. 



The digestive functions of animals, however 

 complex and varied, and however exquisitely 

 contrived to answer their particular objects, yet 

 afford less favourable opportunities of tracing 

 . distinctly the adaptation of means to the re- 

 spective ends, than the mechanical functions. 

 This arises from the circumstance that the pro- 

 cesses they effect imply a refined chemistry, 

 of which we have as yet but a very imperfect 

 knowledge ; and that we are also ignorant of the 

 nature of the vital agents concerned in pro- 



