VALUE OF PROTEIN 



329 



thermometer 

 showing change- 



elements. If living matter is to grow, it must have the proper 

 elements for building. And these it can obtain from food. Pro- 

 teins, although they may 

 be oxidized to release en- 

 ergy, are usually utilized 

 to give the body its nitro- 

 gen, from which, in part, 

 living protoplasm is manu- 

 factured. 



Demonstration 1. Feed two 

 white rats of equal weights 

 for a period on different diet- 

 aries, using in one case an 

 incomplete protein (such as 

 gliadin of wheat) and the 

 other with a complete protein 

 (such as in milk) containing 

 the essential amino acids. A 

 striking contrast may be ob- 

 tained by feeding both with 

 exactly the same foods except 

 that one has a given amount 

 of milk substituted for the 

 same amount of water. Let 

 the class watch the growth 

 of the two animals and report 

 on the final results. Weigh 

 the rats once a week. Keep 

 all conditions except that of 

 food exactly the same for 

 both rats. 



Not all proteins are good 

 tissue builders. Recent 

 feeding experiments have 

 shown that not all proteins 

 are capable of building tissues. 



-wetter around bomb 

 weermect by burnings 

 of food 



A bomb calorimeter. Explain how it works. 



It has been found that the complex 

 chemical substance called protein may be broken by the chemist 

 into simpler proteins called amino acids. Some of these amino acids 

 are useful in tissue building, and others are not. If two rats are fed 

 on diets containing different amino acids, one may thrive, while the 

 other wastes away and dies. For example, gelatin is a very poor 



