DEVELOPMENT. 15 



both animal and vegetable. A plant, like a crystal, can only 

 grow when fresh material is presented to it ; and this is ab- 

 sorbed by its leaves and roots ; and animals for the same pur- 

 pose of getting new matter for growth and nutrition, take food 

 into their stomachs. But in both these cases the materials are 

 much altered before they are finally assimilated by the struc- 

 tures they are destined to nourish. 



Fourthly. The growth of all living things has a definite 

 limit, and the law which governs this limitation of increase in 

 size is so invariable that we should be as much astonished to 

 find an individual plant or animal without limit as to growth 

 as without limit to life. 



Development is as constant an accompaniment of life as 

 growth. The term is used to indicate that change to which, be- 

 fore maturity, all living parts are constantly subject, 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 de- 

 velopment 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 occurrence 

 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 commence- 

 ment. 



It has been already said that the essential features of life 

 are the same in all living things ; in other words, in the mem- 

 bers 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 may 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 manifested 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 capa- 

 bility of the lower kinds of animal to live in this way cannot 

 be entertained; and that such a manner pf life should decide 



