VI. CALORIMETRIC MEASUREMENTS 207 



thermodynamic tables, and the terms "grains of moisture," "foot 

 pounds," and "B.T.U." could then be stored in historical museums. 



2. Calorimetry as Part of Bioenergetics 



Lavoisier demonstrated that animal heat is produced by the com- 

 bustion of organic comj^ounds in the animal body. This was the 

 first major triumph of biocaloi'imetry — life may be regarded and 

 studied as a combustion process. The establishment of such a uni- 

 fying principle in our knowledge of nature is at least as important as 

 the discovery of new phenomena. 



Half a century after Lavoisier's achievement, calorimetry led to 

 an even greater generalization. Robert Mayer noted that work could 

 produce heat or that heat could produce work, and he conceived the 

 idea that heat and work were different manifestations of a common 

 agent that could neither be produced nor destroyed — energy. From 

 the difference in the heat capacity of gases at constant pressure and at 

 constant volume Mayer calculated the caloric equivalent of work. 



Simultaneous measurements of a dog's heat loss, urinary nitrogen 

 excretion, and carbon dioxide production, carried out by Rubner 

 (1894), confirmed Lavoisier's theory concerning the origin of animal 

 heat, and proved that the fundamental law of thermochemistry is 

 applicable to animal metabolism. 



That human work is performed in accordance with the law of con- 

 servation of energy was demonstrated by Atwater and Benedict 

 (1899-1903) with the Atwater-Rosa respiration calorimeter. Among 

 recent accomplishments in biocalorimetry the work of Hill and co- 

 workers on the heat production in muscle and nerve fibers already 

 mentioned (27) is particularly famous. The investigation of Bor- 

 sook and Winegarden (36) also comes to mind. These biochemists 

 applied the second law of thermodynamics to calculate the minimum 

 osmotic work involved in the excretion of urine. They noted that 

 the kidney has a great capacity for w^ork but a low energetic efficiency 

 of 1-2%.* 



3. Outlook 



Energy transformation is one of the most general and fundamental 

 characteristics of life. Biocalorimetry will therefore remain an essen- 

 tial part of physiology. Nutrition at present is dominated by the tre- 

 mendous successes of vitamin chemistry. In some courses and text- 



