586 FUNCTIONS OF ANIMALS. 



knowledge puts it in our power. But were our inquiries con- 

 cerning animals confined to the mere ingredients of which their 

 bodies are composed, even supposing the analysis as complete as 

 possible, our knowledge of the nature and properties of animals 

 would be imperfect indeed. 



How are these substances arranged ? How are they produced ? 

 What purposes do they serve ? What are the distinguishing pro- 

 perties of animals, and the laws by which they are regulated. 



Animals resemble vegetables in the complexness of their struc- 

 ture. Like them, they are machines nicely adapted for particu- 

 lar purposes, constituting one whole, and continually performing 

 an infinite number of the most delicate processes. But neither 

 an account of the structures of animals, nor of the properties which 

 distinguish them from other beings, will be expected here : these 

 topics belong entirely to the-anatomist and physiologist. I mean 

 in the present Division to take a view of those processes only that 

 are concerned in the production of animal substances, which alone 

 properly belong to Chemistry. The other functions are regu- 

 lated by laws of a very different nature, which have no resem- 

 blance or analogy to the laws of Chemistry or Mechanics. 



CHAPTER I. 



OF DIGESTION. 



EVERY living being constitutes a complicated machine, com- 

 posed of a great variety of parts, all of which conspire to produce 

 certain ends calculated for the benefit of the whole. The waste 

 which is continually going on is repaired by the conversion of 

 the food into all the different substances which make up the whole 

 of the living structure. This extraordinary but necessary pro- 

 cess is distinguished by the name of digestion. 



In man and the larger animals the food passes through a num- 

 ber of tubes or canals, and gradually during the course of its 

 progress assumes the form of blood. This blood circulates through 

 appropriate vessels, and supplies the waste of every organ in the 

 body. Bony matter for the bones, muscular matter for the 

 muscles, nervous matter for the brain, &c. or it passes through 

 certain tubes, constituting the matter of which glands are com- 

 posed, and during its progress it is converted into the various se- 



