LIFE, CARBON'S OUTSTANDING PROPERTY 65 



the greatest of ease because it operates by means of traces, 

 of activating substances, known as enzymes or ferments, 

 which can start up the desired chemical changes, even at 

 ordinary temperature. When these activating substances 

 work on carbon compounds they can bring about the most 

 diversified changes on account of the great multiplicity and 

 the complicated make-up of the carbon compounds. The 

 question is not so much whether any chemical changes will 

 occur at all, but precisely in what manner the carbon atoms 

 will be hooked together, or the bonds hooking them together 

 broken and re-arranged. Any new arrangement means a 

 complete change of the substance. In this manner some 

 enzymes perform the most miraculous transformations. 



One enzyme, for instance, the green chlorophyl contained 

 in plant leaves, literally transforms the "clear thin air" into 

 sugar, starch, and other solid material from which the plants 

 build up their bodies. Plants take only a part of their 

 body building material from the ground. Most of it comes 

 from the carbon contained in the air as carbon dioxide, car- 

 bon combined with oxygen. Although only traces of this 

 gaseous carbon compound are contained in the air (about 

 four parts in ten thousand), this diminutive amount is 

 taken from the air by the leaves, and transformed by mere 

 contact with chlorophyl into the solid substances compos- 

 ing the plant body, substances like cellulose, of which wood, 

 one of our best building materials, is largely made up. 



The chemical processes involved in this transformation 

 are little understood; not only carbon dioxide enters into 

 them, but also water vapor. The light rays of the sun are 

 indispensable for these processes as well as certain salts 

 taken from the ground ; but certainly the carbon dioxide gas 

 of the air is the outstanding raw material since it supplies 

 the indispensable carbon for the organic substances of the 

 plant. This transformation of the highly dilute gaseous 

 carbon dioxide is the most important process for all forms 



