THE PRIMARY CONDITIONS OF ANIMAL LIFE H3 



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 organic 

 substances by the following characteristics : Organization ; 

 the power to make over inorganic substances into organic 

 matter, or the changing of organic matter of one kind, as 

 plant matter, into another kind, as animal matter ; motion, 

 the power of spontaneous movement in response to stimuli ; 

 sensation, the power of being sensible of external stimuli ; 

 reproduction, the power of producing new beings like them- 

 selves ; and adaptation, the power of responding to external 

 conditions in a way useful to the organism. Through adap- 

 tation organisms continue to exist despite the changing of 

 conditions. If the conditions surrounding an inorganic 

 body change, even gradually, the inorganic body does not 

 change to adapt itself to these conditions, but resists them 

 until no longer able to do so, when it loses its identity or 

 integrity. 



