Chapter IV

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.