A HISTORY OF METABOLISM 71 



affinity for oxygen than either ingested fat or body fat. . . . Starch behaves like 

 sugar. 



It is established for all time and is and must be correct that the nitrogen- 

 containing materials are the sources of physical power, of the phenomena of 

 motion; also it is equally incontrovertible that fat and the so-called carbohy- 

 drates can yield only heat and never motion. From the foregoing results it 

 follows that the doctrine of Liebig regarding the division of the foodstuffs 

 into plastic and respiratory is correct. 



The authors later suggest the names "dynamogenetic" or "kinetoge- 

 neetic". for "plastic" food substances, and "thermogenetic" for "respira- 

 tory" foodstuffs. 



The extension of the work to man is desirable. It should be known 

 to what extent ingested protein nitrogen appears in his urine as urea or 

 whether it is eliminated in other forms. 



They expect people to say, "It is all self-evident and we have always 

 known these things," and still others to say, "This is not true, here are 

 facts which contradict you." 



It is of great interest to note the affirmation of the doctrine of 

 Liebig in this early work, that though muscle effort was the cause of the 

 metabolism of protein, oxygen caused the destruction of fat and carbo- 

 hydrate up to the limit of the quantity of oxygen available. Both of 

 these doctrines were subsequently overturned by Voit. In the first place, 

 he found, the very same year as that in which he published his work with 

 Bischoff, that muscular work did not increase the protein metabolism of 

 a fasting dog or of one fed with meat. Later he showed the same to be 

 true in the case of a fasting man and of a man fed with a mixed diet 

 containing a liberal amount of protein. He writes: "I maintain this 

 as an incontestable fact. It is of itself so important that I question 

 whether it is desirable to add a word of explanation. The results of a 

 properly conducted and properly appreciated experiment can never be 

 annuled, whereas a theory can change with the progress of science." How 

 quickly came the upsetting of the former assertion, "It is established 

 for all time and is and must be correct that the nitrogen-containing sub- t 

 stances are the sources of physical power, of the phenomena of motion!" 



When I was in the Munich laboratory of Voit and happened to make 

 a positive assertion, the then second assistant, Max Cremer, said to me, 

 "Sagen Sie nicht, Herr Lusk, es ist so ; sagen Sie lieber moglicherweise 

 es kann so sein." Such are the cautious admonitions of those acquainted 

 with history. 



The passing of the conception of oxygen being the cause of the 

 metabolism appears from the following words of Voit(&), written in 1865 : 

 "The conditions of protein metabolism lie in the elementary particles of 

 the organs of the body, which are the hearthstones for all variations and 

 activities. The life of the body is the sum of the action of all the 

 thousands of minute workshops. A combination with oxygen is not first 



