382 VETERINARY PHYSIOLOGY 



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. 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. 

 During the period of active 'digestion the temperature of the 

 blood coming from the liver may be nearly 1 C. higher than 

 that of the blood going to the organ. The liver alone among 

 glandular structures contributes an appreciable amount of 

 heat to the body, since the amount of blood passing through 

 the organ is large, and thus a considerable amount of heat is 

 derived from it. 



C. Brain. Some physiologists have maintained that the 

 fact that the temperature of the brain rises during cerebral 

 activity indicates that the chemical changes going on are 

 sufficient to yield a certain amount of heat. But it is more 

 probable that the rise of temperature is due to the increased 

 flow of blood through the organ, since a study of the gases 

 in the blood coming from the brain gives no indication of any 

 marked increase of chemical change during periods of increased 

 cerebral action. 



2. Regulation of Temperature 



Since heat is constantly being produced, the temperature 

 of the body would tend to rise higher and higher, were 

 there not some arrangement by which just as much heat is 

 eliminated as is .produced, and by which the temperature is 

 thus kept constant. 



