IV. FATE OF THE FOOD ABSORBED 



THE food absorbed may be (A) used immediately as a source 

 of energy, for (1) the Construction or Reconstruction of 

 Tissues ; (2) the Production of Mechanical Work ; (3) the 

 Production of Heat ; 



Or (B) it may be stored for future use in the body. 



The processes of construction and repair of the tissues 

 and the production of mechanical work have already been 

 considered (p. 67 et seq.\ and the production of heat and the 

 regulation of temperature may now be dealt with. 



I. PRODUCTION OF HEAT AND REGULATION OF 

 TEMPERATURE. 



1. Production of Heat. 



A. Muscle. The production of heat in muscle has been 

 already studied (p. G3). It has been shown that muscle, 

 from its great bulk and constant activity, is the main source 

 of heat in the body. Not only may it be demonstrated 

 that the temperature of contracting muscle rises, but it 

 has been found that the temperature of blood coming from 

 the muscles is slightly higher than that of blood going 

 to them. Muscular exercise raises the temperature of the 

 body, and the shivering fit which is induced by exposure to 

 cold is really a reflex reaction by which heat production is 

 increased. Drugs which interfere with muscular contraction, 

 such as curare, diminish the temperature, and young animals, 

 before their muscular tissues become active, have a low 

 temperature unless kept in a warm atmosphere. 



B. Glands. Wherever chemical change goes on in proto- 

 plasm, heat is liberated. Therefore in glands during activity 

 a certain amount of heat is produced, but the production in 

 them is trivial when compared with the production in muscle. 



