394 PROCESSES INFERRED FROM DIRECT OBSERVATION 



available for the production of mechanical work. If we apply these 

 various corrections to the above 'estimate of the work available from 

 the proteins destroyed by Fick and Wislicenus, we find that it 

 actually amounts to only 13,000 kilogram-meters, or less than nine 

 per cent, of the work required merely to lift the weight of their 

 bodies to the top of the mountain. Now it must be remembered 

 that the ascent of their bodies was by no means the whole of 

 the mechanical work which was performed by these experimenters, 

 for apart from the tonus of their skeletal muscles, the work of the 

 secretory and excretory organs, and the movements of the digestive 

 canal, expenditures of energy that cannot very easily be computed, 

 their circulations had to be maintained by the beating of their hearts 

 and their respiratory movements by contractions of the diaphragm and 

 intercostal muscles. These sources of expenditure of energy alone can 

 be estimated to have accounted for no less than 30,000 kilogram-meters 

 of work during the ascent of the mountain. All the energy actually 

 procurable from the protein they decomposed, therefore, would not 

 have half sufficed to maintain the respiratory movements and the 

 heart-beat, leaving nothing over whatever for the ascent of the moun- 

 tain. The proportion of muscular energy furnished by the proteins 

 must therefore have been very small. 



That under normal conditions the whole of the energy consumed in 

 muscular exertion is derived from non-protein sources, is rendered 

 very probable by the discovery of Voit, that work upon the treadmill 

 by a dog fed upon mixed rations does not increase the nitrogen output. 

 Not only is the total nitrogen output unaffected by muscular work 

 upon a mixed diet, but the entire Protein Metabolism pursues its normal 

 course, undisturbed by the large expenditure of energy which is occur- 

 ring. This is shown by an experiment by Shaffer, who investigated the 

 urine of a man fed upon a purine-free diet, containing a minimal allow- 

 ance of nitrogen, in three different periods, namely, a rest-period of 

 six days which he spent in bed; a normal period of five days which he 

 spent in performing light work about the laboratory, and a work period 

 of four days in which he added to the laboratory work long daily walks. 

 The following were the results obtained : 



The question arises, however, whether, if placed under practical 

 compulsion to do so, by the scarcity or absence of other source of 



