Normal Processes of Energy 

 Metabolism 



JOHN E. MUELIN 



ROCHESTER 



It is a familiar fact that the temperature of what we call "warm- 

 blooded" animals is not only several degrees higher than the average tem- 

 perature of the atmosphere, hut it is held constantly at this level despite 

 fluctuations of the environing temperature. So-called "cold-blooded" ani- 

 mals likewise produce heat, the difference being that in these the body 

 temperature is not regulated but is dependent upon the external temper- 

 ature. All animals therefore are transformers of energy. In fact experi- 

 ence and theory are in accord in regarding the production of heat as a neces- 

 sary consequence of the phenomena of life; it is a sign, indeed, of vital 

 activity. 



There are two general methods of measuring the production of heat: 

 (1) by determining the intensity of the chemical processes (combustion) 

 by which heat is liberated in the organism ; and (2) by registering directly 

 the heat disengaged by the organism in a calorimeter. The first is known 

 as the indirect or chemical method; the second, the direct or physical 

 method. 



A. Indirect Calorimetry 



The indirect or chemical method depends upon the successful measure- 

 ment of the respiratory exchange. We must, therefore, consider at 

 some length the technology of this subject. In the meantime it may 

 be stated that the indirect method of calorimetry offers certain ad- 

 vantages over the direct method. When the latter subject is con- 

 sidered (page 567) it will be evident that in order to measure all of the 

 heat discharged from the animal body by the several routes of escape a 

 rather complicated apparatus is necessary. In time this may be simplified, 

 but at present an accurate calorimeter is far more complex and far more 

 costly both in initial cost and for operation than a respiration machine. 

 Secondly, the indirect method is more accurate as matters now stand. 

 Krogh(c) finds that he can measure oxygen absorption with his micro- 

 respiration apparatus to an accuracy of 2 cu.mm. of O 2; equivalent to 10 



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