188 NUTRITIONAL PHYSIOLOGY 



When it had become plain that muscular contractions 

 must involve increased destruction of material, the ques- 

 tion arose as to the nature of the substance sacrificed. 

 Chemical teaching in the middle of the nineteenth century 

 was dominated by the influence of Liebig. It was his view 

 that the performance of muscular work could be supported 

 only by the consumption of protein. The impression 

 was a natural one, since muscle is so largely composed of 

 protein. He recognized that carbohydrates and fats were 

 oxidized in the respiratory process, but held that heat 

 alone and not movement resulted from their metabolism. 

 The distinction which Liebig attempted to draw between 

 the service of protein and non-protein material was des- 

 tined to be wiped out in consequence of a certain memorable 

 trial. The reference is to the so-called "Faulhorn experi- 

 ment" of Fick and Wislicenus. 



By the year 1860 the conception of the convertibility 

 of energy from one form to another had become familiar. 

 A valuable datum, the mechanical equivalent of heat, had 

 become available. (One calorie is equal to the energy 

 consumed in raising 426.5 kilograms 1 meter.) The fuel 

 values of a number of substances were known. Two young 

 scientists, Fick and Wislicenus, conceived a project for 

 testing the prevailing belief in the unique service of pro- 

 tein as the support of muscular activity. They knew that 

 the nitrogen of the urine would afford the approximate 

 measure of the protein undergoing destruction in a given 

 interval. If a known 'amount of work were done it would 

 be possible to find out whether the protein consumed in 

 the same time would account for all of it. 



They ascended the Faulhorn, a mountain rising 1956 

 meters above the lake at its foot. In reaching the top 

 each experimenter must have done an amount of work 

 represented by the product of his weight by the vertical 

 height attained. (Much additional work must have been 

 done also by the heart, the breathing muscles, and in the 

 execution of other movements for which no credit is 

 given in the calculation.) The figured work, therefore, 



