LIFE AS MECHANISM 



the method was complicated, but the chemist certain- 

 ly never considered urea as alive. The chemist can 

 also create water from hydrogen and oxygen, and 

 why do not biologists include this amongst the or- 

 ganic processes; it is as much a waste product of the 

 organism as is urea; so, also, is carbon dioxide. Is it 

 so surprising that the living chemist by means of his 

 brains and hands can make compound substances 

 which are the same as those made in the laboratory 

 of the living cell *? But where, and what, are the chem- 

 ists of that laboratory*? 



As a rather simple example, let us study the prop- 

 erties of the growing plant. The leaves of a plant con- 

 tain a substance called chlorophyll whose chemical 

 composition is said to be known. When light falls on 

 the living leaf, chlorophyll in some way can break up 

 the carbon dioxide of the air which comes into contact 

 with it into free oxygen and free carbon ; the oxygen is 

 given back to the air but the carbon is retained in the 

 living plant to form its bulk. But when light falls on 

 chlorophyll in a dead leaf, or extracted from a plant, 

 no such action occurs. And curiously enough, at a de- 

 finite season of the year, the chlorophyll decomposes 

 and the leaf turns yellow. Botanists say they under- 

 stand these processes and that they are chemical, as the 

 following anecdote proves. An eminent botanist gave 

 this lucid explanation to the question, why green 

 leaves turned yellow in the autumn. His answer was 

 that, in the spring, leaves contain chlorophyll, and, 



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