THE LIVING ORGANISM 27 



Our very substance with its energies has been wrested 

 from the environment ; and as we, like all other living 

 things, must replenish our tissues as we wear out in the 

 very act of living, we cannot cease to maintain the 

 closest possible relations with the environment with- 

 out surrendering our existence in the battle of life. 



From the foregoing discussion, it will be evident, I 

 am sure, that there is ample justification for the biologi- 

 cal dictum that a living individual is a mechanism. 

 Not only is the organism composed always of cell 

 units grouped mechanically in tissues and organs and 

 organic systems ; not only are the operations which 

 make up its hfe constant and regular under similar 

 conditions ; not only is the whole creature mechanically 

 connected with the inorganic world ; but above all the 

 whole activity of a biological individual is concerned 

 necessarily and again mechanically with the acquisition 

 of materials endowed with energy, which materials and 

 energy are mechanically transformed into Hving matter 

 and its life. Even though an organism is so much 

 more complex than a locomotive, and so plastic, never- 

 theless, in so far as both are mechanisms, the conception 

 of the evolution of the former may be much more readily 

 understood through a knowledge of the historical trans- 

 formation of the latter. 



What, now, is life? To most people '4ife seems to 

 be something which enters into a combination of carbon 

 and hydrogen and the other elements, and makes this 

 complex substance, the protoplasm, perform its va- 

 rious activities." Nearly every one finds it difiScult 



