THE ORGANIC AND THE INORGANIC 295 



of degree, and not of kind, they are not essential, 

 are not differences at all ? Must we say, for instance, 

 that although an animal is a much more efficient 

 machine than a gas-engine (in the sense of efficiency 

 as understood by the engineer) , there is really no 

 difference between them, that they are both thermo- 

 dynamic mechanisms, since in both energy is dissipated ? 

 Ought we to say that, because the last steps in the 

 formation of urea in the animal body are synthetic 

 ones, there is really no difference between the nature of 

 the energy-transformations that occur in the animal 

 and the plant modes of metabolism ? Ought we to say 

 that, because a dog may sometimes act intelligently 

 and a man instinctively, psychically they are similarly- 

 behaving organisms ? Surely this amounts to saying 

 that, because things are not absolutely different, they 

 are the same ; and surely the mode of reasoning is a 

 vicious one ! 



What we clearly see in the different kinds of organ- 

 isms — in the metabolically constructive plant and the 

 metabolically destructive animal ; or in the instinc- 

 tively-acting Arthropod and the intelligently-acting 

 Mammal — is the progressive development of different 

 tendencies. If the green plant is, in its essence, the 

 same kind of physico-chemical constellation as is the 

 animal, yet the tendency of its evolution has been that 

 more and more it has acquired the habit, or the power, 

 of using solar radiation to combine together carbon 

 dioxide, water, and nitrogenous inorganic salts to form 

 proteid and carbohydrate substances. On the other 

 hand, the tendency of the animal has been more and 

 more to absorb into its own tissues the proteid and 

 carbohydrates synthesised by the green plant, and 

 then to break these substances down into carbon 

 dioxide and water, and less and less to effect such 



