LECTUEE III. 

 THE CRITERIA OF LIVINGNESS. 



§ 1. Living and Not-living. § 2. The Essential Characteristics of 

 Living Organisms. § 3. Persistence of a Complex Specific 

 Metabolism and of a Corresponding Specific Organisation. § 4. 

 The Capacity of Growth, Reproduction, and Development. 

 § 5. Effective Behaviour, Registration of Experience, and 

 Variability. 



§ 1. Living and Not-living. 



If we are to reach a coherent view of Nature, such as 

 could be included in a philosophy, we must arrive at some 

 discernment of the characteristics which mark off living 

 organisms from their not-living surroundings. In the pres- 

 ent state of science a definition of the organism cannot be 

 more than tentative, but it must be continually attempted. 



When we pass from watching a flowing stream or the 

 wind-swept clouds, to look at the bees visiting the flowers, 

 or the swallows building their nest, we feel that we are 

 facing something new — living. What we see is not, indeed, 

 in every respect new as compared with the inorganic, for 

 gravity acts on animals just as on drops of rain, and living 

 creatures never disobey, so far as we know, the ordinary 

 laws of physics and chemistry which sum up the routine 

 of our analytic experience of the not-living. On the whole, 

 however, especially if we look at animals rather than plants, 

 the differences impress us more than the resemblances, 

 we feel rightly that we are in the presence of something 

 new. Organisms show characteristics which mark them off 



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