14 DOCTRINE OF EVOLUTION 



lieved by science to be the basis of the second and the 

 third ; but this matter of chemical constitution must take 

 its proper place in the series of structural characters, 

 which we shall discuss further on as we develop the 

 conception of organic mechanism. 



Whatever definition we may employ for a machine 

 or an engine, we cannot exclude the hving organism 

 from its scope. As a "device for transforming and 

 utilizing energy" the hving organism differs not at all 

 from any "dead" machine, however complex or simple. 

 The greatest lesson of physiological science is that the 

 operations of the different parts of the hving thing, as 

 weh as of the whole organism itself, are mechanical; 

 that is, they are the same under similar circumstances. 

 The hving creature secures fresh supplies of matter and 

 energy from the environment outside of itself; these 

 provide the fuel and power for the performance of the 

 various tasks demanded of an efficient living thing, 

 and they are the sources upon which the organism 

 draws when it rebuilds its wasted tissues and replenishes 

 its energies. The vital tasks of all organisms must be 

 considered in due course, but at first it is necessary to 

 justify our analogies by analyzing the structural char- 

 acteristics of animals and plants, just as we might 

 study locomotives in a mechanical museum before we 

 should see how they work upon the rails. 



Among the familiar facts which science reveals in a 

 new light are the peculiarly definite qualities of living 

 things as regards size and form. There is no general 

 agreement in these matters among the things of the 

 inorganic world. Water is water, whether it is a drop 

 or the Pacific Ocean ; stone is stone, whether it is a 



