FOOD 



239 



the breaking down of their molecules into simpler com- 

 pounds (waste substances), may occur at any point above 

 the carbohydrate stage, as is indicated by the arrowed 

 lines that run across the diagram from left to right. Yet 

 some of the food, of course, is destined to continue in the 

 process of elaboration until it becomes a part of the proto- 

 plasm itself. For the protoplasm itself is constantly break- 

 ing down and must constantly be renewed. Now you can 

 see why it is believed to be true, as you have probably 

 heard, that at the end of seven years every part and par- 

 ticle of the human body has been changed, so that nothing 

 which was there seven years ago is there now; in most 

 of the body the changes or replacements are even more 

 rapid. Now, too, you can understand better what was 

 meant by the statement that life is a procession of changes. 

 Huxley said of protoplasm that it is like a whirlpool in that 

 it is ever changing, yet still the same. 



On the descending side of the circle you get new evidence 

 of the immense importance of bacteria. Here they appear 

 as the chief assistants to the process of oxidation in com- 

 pleting the cycle, in reducing dead and waste organic 

 stuff to the inorganic state again. What would be the 

 disadvantage to life in case the cycle were not complete 

 at this point? 



The Artificial Manufacture of Food. Physics and 



chemistry are commonly considered to be those branches of 

 science that have contributed most to man's convenience. 

 But as you study this diagram and consider its significance, 

 do you not see that the greatest invention of the future 

 will be the invention of a biologist? Physics and chem- 

 istry will continue to contribute much to man's convenience, 



