INTRODUCTION 17 



The proteins are complex compounds of high molecular weight. 

 They are built up of amino acids. The simplest formula for 

 oxyhemoglobin, a protein of the red blood corpuscles, is 

 C658Hii8iN207S 2 Fe02io equivalent to a molecular weight of 

 15,455. Compare this with a formula of C12H22O11 and a mo- 

 lecular weight of 342 for cane sugar. 



Nucleic acid also is a chemical compound with large mole- 

 cules. It appears to be built up of sugar, phosphoric acid, and 

 certain nitrogenous bases. The formula for yeast nucleic acid is 

 C38H49O29N15P4, equivalent to a molecular weight of 1303. 



It is evident, therefore, that even in an organism where 

 growth appears to be a simple process it is a very complex one 

 and one with which we are not yet fully acquainted. The biolo- 

 gist assumes for his working plan that the construction of living 

 protoplasm and other body parts takes place according to known 

 or discoverable laws of physics and chemistry. Parts of the proc- 

 ess can be imitated in a test tube, but its entirety remains a secret, 

 possibly one which we may never discover. We must agree with 

 Aristotle when he says, "Wherefore one should not be child- 

 ishly contemptuous of the most insignificant animals, for there 

 is something marvelous in all natural objects." 



The questions raised in the discussion of growth thus far 

 would appear to make the problem of growth sufficiently com- 

 plicated, but there is still another important essential in the 

 process. The construction of new protoplasm, new cell walls, 

 and new body parts requires energy in somewhat the same way 

 that energy, in the form of muscular work by masons, is neces- 

 sary for the construction of a brick house from bricks. The 

 energy used in growth is that present in the food materials. It 

 is set free by their destruction in a manner somewhat similar to 

 the way in which the energy in coal is set free in its destruction 

 by burning. We call the process by which a living organism sets 

 free the energy stored in. food materials respiration, and for 

 most plants and animals oxygen from the air is used in respira- 

 tion, and water and the gas carbon dioxide are formed. In such 



. I I I K R A R Y 



