280 ITS BEARING ON MEDICAL PRACTICE. 



4. From the three i^receding statements it is easy to see that, for 

 every gram of proteine consumed, 0.8416 heat units are contained in 

 the urea excreted ; so that — 



The digestion of 1 gram of jproteinc gives out 4.8375 heat-units. 



It is easy to see that 501.28 grains of urea excreted correspond to 

 1,050 grains of proteine in the food, or to 106.92 grams; and the total 

 "work due to the digestion of this quantity of food mnj be found by mul- 

 tiplying it by the '■'■digestiQn coefficient " already found, and by 423, which 

 is Joule's coefficient for converting heat-units into kilogram-meters. 

 Hence we have — 



Work due to production of 501.28 grains of urea 

 = 100.92 X 4.8375 x 423 = 218786 kilogram-meters = 704 foot-tons. 



This amount of theoretical "work produced by nitrogenous food is 

 double the work actually done during the walking excursion. 



The average work was 20.74 miles horizontal per day, which may be 

 considered as the exact equivalent of lifting my weight (knapsack and 

 clothes included = 150 pounds) through one mile of vertical height. 

 Hence the work actually done by me was — 



l^iAi^= 354 foot-tons. 

 2240 



This amount of muscular work accounted for almost exactly half the 

 whole theoretical work supplied by the food that goes to form urea, viz, 

 704 foot-tons. But it has been already shown that 2 grains of urea per 

 pound of body weight is required to maintain the vital work, including 

 circulation and respiration ; this would give (since I weighed 128 pounds) 

 256 grains of urea required for vital work, or almost exactly half of the 

 501.16 grains excreted, so that one-half of the available work might be 

 considered as expended on vital work, and the other half as expended 

 on external muscular work. This supposition, however, requires us 

 to believe that the muscles act without loss by friction. This is not 

 admissible, for I have elsewhere endeavored to show that there is a loss 

 in the force applied by the muscles of various animals, in consequence 

 of the frictiou of their tendons, amounting on the average, in man, to 35 

 per cent., and in the mastiff, to 41 iJer cent. 



Hence it may be regarded as certain that the available force repre- 

 wsented by 501 grains of urea is not sufficient to account fully both for 

 vital work and for the external mechanical work expended by me during 

 the experiments just described. 



The foregoing observations and calculations were made in the month 

 of July, 1866, bat I did not then publish them, as I found afterward 

 that I had been anticipated by Dr. Ficlc and Dr. Wislicenus, of Zurich, 

 in a paper published in June in the Philosophical Magazine, on the urea 

 excreted during an ascent of the Faulhorn. Professor Frankland, in a 

 paper published in the same journal in September, 1866, corrected some 

 erroneous reasoning that found its way into Fick and Wislicenus's 

 paper, and further supplied, from direct experiment, the digestion coeffi- 



I 



