DISTINCTIVE CHAKACTEKS OF LIVING BEIXGS. ' 3 



governs this limitation of increase in size is so invariable that we 

 should be as much astonished to find an individual plant or animal with- 

 out 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, before 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 merely 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. 



Differences between Plants and Animals. 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 king- 

 doms. It may be w r ell to notice briefly the distinctions which exist be- 

 tween 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. 



(1.) Perhaps the most essential distinction is the presence or absence 

 of power to live upon inorganic material. By means of their green color- 

 ing matter, chlorophyl a substance almost exclusively confined to the 

 vegetable kingdom, plants are capable of decomposing the carbonic acid, 

 ammonia, and water, which they absorb by their leaves and roots, and 

 thus utilizing them as food. The result of this chemical action, which 

 occurs only under the influence of light, is, so far as the carbonic acid is 

 concerned, the fixation of carbon in the plant structures and the exhala- 

 tion of oxygen. Animals are incapable of thus using inorganic matter, 

 and never exhale oxygen as a product of decomposition. 



The power of living upon organic as well as inorganic matter is less 

 decisive of an animal nature; inasmuch as fungi and some other plants 

 derive their nourishment in part from the former source. 



(2.) There is, commonly, a marked difference in general chemical 

 composition between vegetables and animals, even in their lowest forms; 

 for while the former consist mainly of cellulose, a substance closely allied 

 to starch and containing carbon, hydrogen, and oxygen only, the latter 

 are composed in great part of the three elements just named, together 

 with a fourth, nitrogen; the chief proximate principles formed from 

 these being identical, or nearly so, with albumen. It must not be sup- 

 posed, however, that either of these typical compounds alone, with its 

 allies, is confined to one kingdom of nature. Nitrogenous compounds 



