NATURE OF LIFE AND LIVING MATERIAL 5 



Growth and Repair: A body that is alive increases in size some 

 time during its period of living. The growth of a living body is due 

 to an actual increase in the quantity of living materials, formed by 

 life processes from quite difiFerent substances derived from its sur- 

 roundings. Crystals and other non-living objects also grow, but the 

 increase is largely as added layers, external and local. Repair of 

 injury, a special type of growth, is solely a property of living ob- 

 jects. No non-living body can repair damage brought about by some 

 incident in its surroundings. 



Reproduction: Every normal living object at some time during 

 its life is capable of partaking in the reproduction of another body 

 also alive and very much like itself. In general, conditions within 

 the organism bring about reproduction. The property is peculiar 

 as to method in living objects and is a critical test of life. 



Organization and Correlation: Living objects always consist of 

 a very definite arrangement of a peculiarly organized substance 

 called PROTOPLASM. The protoplasm is further organized into small 

 units termed cells, recognizable as such regardless of the size of 

 the plant or animal and of its other characters. Structural organiza- 

 tion in the body of a plant or animal is indissociably linked with 

 its properties of contractility, growth, reproduction, and so on, as 

 many types of machines in a factory are correlated for the produc- 

 tion of a common result. A living object is an individual of definite 

 size, its parts so correlated that the whole operates as a balanced 

 unit. Non-living objects, for example, a rock, may vary in size from 

 a very minute to a very large body; but a bird, for instance, does 

 not become indefinitely large, nor does it exist as a bird in a very 

 minute size. The internally directed control that unifies the organ- 

 ism as to size, structure, and activity, is a character that is not 

 duplicated in the non-living. 



Mechanism and Vitalism. All these are evidences of activ- 

 ity and indicate that some sort of force is operating in living ma- 

 terial. The question at once arises: What is the nature of this force 



