4 AXIMALS CONTRASTED 



which, before maturity, all living parts are constantly sub- 

 ject, and by which they are made more and more capable 

 of performing their several functions. For example, a 

 full-grown man is not simply a magnified child; his tissues 

 and organs have not only grown, or increased in size, they 

 have also developed, or become better in quality. 



No very accurate limit can be drawn between the end of 

 development and the beginning of decline ; and the two 

 processes may be often seen together in the same individual. 

 But after a time all parts alike share in the tendency to 

 degeneration, and this is at length succeeded by death. 



The decline of living beings is as definite in its occur- 

 rence as growth or development. Death not by disease 

 or injury so far from being a violent interruption of the 

 course of life, is but the fulfilment of a purpose in view 

 from the commencement. 



It has been already said that the essential features of 

 life are the same in all living things ; in other words, in the 

 members of both the animal and vegetable kingdoms. It 

 may be well now to notice briefly the distinctions which 

 exist between the members of these two kingdoms. It 

 aaay seem, indeed, a strange notion that it is possible to 

 confound vegetables with animals, but it is true with 

 respect to the lowest of them, in which but little is mani- 

 fested beyond the essentials of life, which are the same in 

 both. 



I. Perhaps the most essential distinction is the presence 

 or absence of power to live upon inorganic material ; in 

 other words, to act chemically on carbonic acid, ammonia 

 and water, so as to make use of their component elements 

 as food. Indeed one ought probably to say that a question 

 concerning the capability of the lower kinds of animal to 

 live in this way cannot be entertained; and that such 

 a manner of life should decide at once in favour of a 

 vegetable nature, whatever might be the attributes which 

 seemed to point to an opposite conclusion. The power of 



