CHAPTER IV. Source of the Energy of Muscle Work, With Some Theories of

SOURCE OF THE ENERGY OF MUSCLE WORK, WITH SOME THEORIES OF PROTEID METABOLISM 119

TOPICS: Relation of muscle work to energy exchange. Views of Liebig. Experimental evidence. Relation of nitrogen excretion to muscle work. Significance of the respiratory quotient in determining nature of the material oxidized. Fats and carbohydrates as source of energy by muscles. Utilization of proteid as a source of energy. Formation of carbohydrate from proteid. Significance of proteid metabolism. Theories of Carl Voit. Morphotic proteid. Circulating proteid. General conception of proteid metabolism on the basis of Voit’s theories. Pflüger’s views of proteid metabolism. Rapidity of elimination of food nitrogen. Methods by which nitrogen is split off from proteid. Theories of Folin. Significance of creatinin and of the percentage distribution of excreted nitrogen. Endogenous or tissue metabolism. Exogenous or intermediate metabolism. Needs of the body for proteid food possibly satisfied by quantity sufficient to meet the demands of tissue or endogenous metabolism. Bearings of Folin’s views on current theories and general facts of proteid metabolism. Large proteid reserve and voluminous exogenous metabolism probably not needed. Importance of feeding experiments in determining the true value of different views.