22 FINAL CAUSES. 



the genera, the families, the orders, and the classes 

 of those beings ; and, lastly, as they concern the 

 whole collective union of the organized world. 



These peculiar laws, which it is the province 

 of physiology to investigate, are, as I have 

 before observed, of two kinds, each founded 

 upon relations of a different class. The first, 

 which depend upon the simple relation of cause 

 and effect, are concerned merely with the natural 

 powers of matter. They are the laws that 

 regulate the succession of phenomena purely 

 physical in all their stages. These phenomena 

 consist in changes among material particles, 

 which are either of a mechanical or chemical 

 nature ; or in the affections of imponderable 

 physical agents, such as heat, light, electricity, 

 and magnetism ; and they include also the 

 phenomena that take place in organized bodies, 

 and which are referable to the operation of cer- 

 tain physical powers, appertaining to particular 

 structures, such as muscular contraction and 

 nervous irritation ; phenomena which, as we 

 shall afterwards find, are not reducible to any 

 of the former laws, but are peculiar to the living 

 state. The second class of laws comprise those 

 which are founded on the relation of means to an 

 end ; and w hich are usually denominated fi7ial 

 causes. They involve the operations of mind, in 

 conjunction with those of matter. They pre- 

 suppose intention or design ; a supposition which 



