584 



JOHN R. MUELTN 



designation of ^basic principles." Some indeed are so fundamental and 

 so universal in their application as to deserve the designation, "laws of 

 metabolism." But it will avoid controversy to employ the more conserva- 

 tive term. 



I. The Principle of the Conservation of Energy 

 in the Animal Organism 



Lavoisier, the father of metabolism, foresaw that the heat of the 

 animal body could be measured by two means : the computation based upon 

 the chemistry of combustion, and direct measurement (Gavarret), and it is 

 almost certain that had he been permitted to complete his researches in this 

 field the demonstration of complete agreement by the two methods would 

 have lain to his credit. Without following the historical development of the 

 subject or recording the failures which intervened \ve may pass at once to 

 the work pf Rubner(^). With the calorimeter just described Rubner 

 studied the heat production of dogs by the two methods. He determined 

 the C and X of the excreta and computed the amount of protein and fat 

 metabolized in fasting and after feeding with meat and lard. Multiplying 

 the protein and fat by the physiological heat values of these foodstuffs re- 

 cently determined by him (page 551) he obtained the heat production by 

 and indirect method. At the same time his calorimeter recorded the actual 

 amount of heat eliminated. His results are given in Table 11. 



TABLE 11 

 HEAT PRODUCTION OF Docs BY DIRECT AND INDIRECT CALORIMETRT (Rubner) 



In a total of forty-six days of experimentation, with his animals Rubner 

 thus found a difference of only 0.3 per cent between the heat production 

 as calculated and the heat production as directly measured. This proves 

 that the energy set free by oxidation (in the absence of external work), 

 whatever transformations it may undergo in the body, finally leaves the 

 body as heat. In other words, all the available energy which entered the 

 body in potential form has been recovered as heat, and the applicability 



