CONDITIONS OF ANIMAL LIFE 3 



stances for food instead of organic, are characteristics 

 readily observed and practically characteristic of many- 

 celled plants! When the thousands of kinds of one-celled 

 organisms are compared, however, it is often a matter of 

 great difficulty or of real impossibility to say whether a 

 given organism should be assigned to the plant kingdom 

 or to the animal kingdom. In general the distinctive 

 characters of plants are grouped around the loss of the 

 power of locomotion and related to or dependent upon it. 



3. Living organic matter and inorganic matter. It would 

 seem to be an easy matter to distinguish an organism that 

 is, a living animal or plant from an inorganic substance. 

 It is easy to distinguish a dove or a sunflower from stone, 

 and practically there never is any difficulty in making such 

 distinctions. But when we try to define living organic mat- 

 ter, and to describe those characteristics which are peculiar 

 to it, which absolutely distinguish it from inorganic matter, 

 we meet with some difficulties. At least many of the char- 

 acteristics commonly ascribed to organisms, as peculiar to 

 them, are not so. The possession of organs, or the composi- 

 tion of the body of distinct parts, each with a distinct func- 

 tion, but all working together, and depending on each other, 

 is as true of a steam-engine as of a horse. That the work 

 done by the steam-engine depends upon fuel is true ; but 

 so it is that the work done by the horse depends upon fuel, 

 or food as we call it in the case of the animal. The oxida- 

 tion or burning of this fuel in the engine is wholly compar- 

 able with the oxidation of the food, or the muscle and fat 

 it is turned into, in the horse's body. The composition of 

 the bodies of animals and plants of tiny structural units, 

 the cells, is in many ways comparable with the composition 

 of some rocks of tiny structural units, the crystals. But 

 not to carry such rather quibbling comparisons too far, it 

 may be said that organisms are distinguished from inorganic 

 substances by the following characteristics : Organization ; 

 (jihe power to make over inorganic substances into organic 



