126 FUNDAMENTALS OF STRUCTURE AND FUNCTION 



the first simple microscopes of the Dutchman, Antony van Leeuwen- 

 hoek, but enormous advances have been made in this period. The 

 most rapid advances in chemistry, physics, and biology have come 

 in the last two or three decades, but we are still far from the solution 

 of the great riddle of the universe — What is life, and from whence 

 did it come ? 



What Is Being Alive? 



The chemist or the biologist weighs the food an organism eats and 

 thus finds out that much of the energy locked up in food is trans- 

 formed within the body of the organism, ultimately to be released 

 in another form, either in heat production or in work of some kind. 

 Not only do living things release energy but they also grow and are 

 able to repair parts that are wasted or lost. Think of the athlete, 

 hale and hearty, winning points for his team ; losing weight in a 

 football game, making it up after the game at the training table, or 

 imagine the same athlete recovering from a severe illness, or with 

 his leg in a cast after an accident. One may feel fairly sure that he 

 will soon be well again. The living stuff of which he is made will 

 not only use the food to release energy for his normal processes, but 

 will also rebuild the expended body material and rid itself of such 

 wastes as result from the process. Put in another way, this living 

 stuff of which an athlete is composed has the ability to take in food, 

 to use this food for the release of the energy stored up in it, or, under 

 certain conditions, to make some of the food over into living ma- 

 terial. Living things thus have the capacity for growth, for waste 

 and repair, and, like man-made machines, have the abihty to use food 

 fuel, and to release energy from it. 



Metabolism 



The sum total of all the processes involved in the business of being 

 alive is called metabolism. This series of processes is twofold : first, 

 constructive metabolism, or anabolism, in which the food material 

 becomes a part of the living organism, the energy being held there in 

 a potential form ; and second, by destructive metabolism or katabo- 

 lism, in which the body material is broken down to release energy, 

 and in which, as a result, there is the production of work and a 

 passing off of waste products. This text is concerned, by and large, 

 with the various phases of metabolism which will be considered in 

 greater detail later. 



