32 THE FOUNDATION Part I 



persons as contrasted with its success between identical twins. The variety 

 of proteins is no less remarkable than their constancy. One remembers the 

 whales that after thousands of years in the ocean still have blood proteins 

 similar to their near kin on land. In the inheritances of plants and animals 

 proteins have not only kept their basic patterns for millions of generations, 

 but countless variations have been added, making their constancy all the 

 more remarkable. 



Enzymes, Vitamins, and Hormones. These are associated with other sub- 

 jects that are discussed later, the first two with foods and digestion, the 

 hormones with endocrine glands. All known enzymes and many of the vita- 

 mins and hormones are proteins or intimately associated with proteins and 

 all are catalysts. 



Enzymes are vital ^catalysts of living matter affecting the rate, and even 

 initiating chemical reactions of all cells. Their importance is realized in light 

 of the fact that they participate in the breaking down of proteins into amino 

 acids, of starch molecules into simple sugars, and of fats into fatty acids and 

 glycerol before any one of them can go through a cell membrane (Fig. 3.3). 



Characteristics of Protoplasm 



The physical basis of life is made of common materials largely composed 

 of a few of the most abundant substances in the earth and atmosphere, all 

 of them easily attainable. Its organization is in the highest degree complex, 

 a continuous series of reactions which follows a permanent general pattern 

 with details that are related to particular surroundings. It has its own char- 

 acteristic organization and punctuality, precision of arrangement, and inter- 

 dependence of parts. Plants and animals exist in multitudinous variety yet 

 they are fundamentally similar. They all have the capacity for the composite 

 of continual chemical changes called metabolism. 



Protoplasm has a capacity to change and yet hold its stability: in its con- 

 tent of water, an almost universal solvent; in its abundance of proteins; in 

 its colloid structure, with variability in size and shape of particles allowing 

 large total areas of exposure to surrounding influences and subject to con- 

 tinuous movement. It is susceptible to external and internal influences and 

 consequent shifts in the phases sol and gel. It has rhythms and continuity of 

 income and outgo of materials, resulting in a balance maintained between 

 constructive and destructive changes. 



Cells 



Cells are the units of the architecture of plants and animals. A cell is a 

 bit of protoplasm containing a nucleus without which it cannot grow or re- 

 produce itself (Fig. 3.4). As long as it lives the cell constantly builds and 

 burns in the unceasing chemical changes of metabolism. 



