xviii INTRODUCTION. 



Of living bodies there are two great divisions, the Vege- 

 table and the Animal. In the vegetable there is life, but, so 

 far as we know, there is no sensation, nor power of motion 

 dependent upon the will. In the animal there is sensation, 

 and the power of voluntary motion. An aphorism frequently 

 quoted is, that plants grow and live ; that animals grow, live, 

 and feel. Life, then, pervades both kingdoms ; but life, in the 

 animal, performs other functions, and sensation is added to 

 the powers merely vital. 



Besides that distinction between common matter, and mat- 

 ter under the influence of the vital principle, which is founded 

 on the different powers and functions of bodies, there is an- 

 other distinction, obvious to the senses, founded on the dif- 

 ferent structure and form of the bodies. Matter uninfluenced 

 by the powers of life, presents itself in masses, or in regular 

 forms termed crystalline. In living bodies, the particles con- 

 stituting the organism do not arrange themselves in masses 

 or crystals, but form fibres, sacs, tubes, or other parts, suited 

 to particular functions. This structure is termed organiza- 

 tion, and is proper to the living kingdom, vegetable and ani- 

 mal. Hence the further distinction exists between the mine- 

 ral and living kingdoms of nature, of Organic and Inorganic. 

 Inorganic matter has its substance increased by the addi- 

 tion of further particles. Organic matter is likewise increas- 

 ed by the addition of further parts, but then it adds to its 

 own substance by the action of its proper organs. A mineral 

 is increased in volume or weight by the simple addition of 

 new parts : a plant, or an animal, deriving matter from other 

 substances, converts it, by the action of its organs, into the 

 various tissues which constitute its own substance. Organic 

 bodies, therefore, only can be said to grow. 



As the particles of living bodies are determined and con- 

 trolled in their actions and relations by peculiar forces, so 

 living bodies resist changes, physical and chemical, which, in 

 the dead state, would take place. The influence of heat, 

 moisture, or other agents, which would subvert the union of 



