NORMAL PROCESSES OF ENERGY METABOLISM 583 



consists of a constant temperature bath of water in which the respiration 

 chamber is immersed. A cushion of air immediately surrounds the cham- 

 ber whose walls are of metal. The heat of the animal's body (dog) passes 

 readily through the metal and causes the air to expand. The expansion is 

 recorded by means of a spirometer which registers its movements graphi- 

 cally on a white surface (in Fig. 31 two spirometers may be seen on a shelf 



Fig. 31. The second calorimeter of Rubner. Description in the text. 



back of the calorimeter). As a control mechanism another spirometer 

 registers in the same manner the summated expansion of four vertical 

 air-cushions in the four corners of the water bath isolated from the first 

 air-cushion. Fluctuations due to variations of temperature from ex- 

 traneous causes or to variations of barometric pressure are thereby con- 

 trolled. 



C. Basic Principles of Energy Metabolism 



Only the most important generalizations concerning the energy metabo- 

 lism in normal warm-blooded animals will be attempted here. While some 

 of these are not yet universally accepted, sufficient evidence is at hand in 

 the case of all of those which will be discussed to dignify them with the 



