436 OF NUTRITION. 



348. The amount of work done by the body may be divided into 1. Cal- 

 orific work ; 2. Internal mechanical work, such as is required for the main- 

 tenance of the circulation, respiration, digestion, etc.; 3. External mechani- 

 cal work, expended in the movements of locomotion, lifting and carrying 

 weights, etc.; 4. Mental work ; and lastly, in youth, the work of growth. 

 The absolute amount of heat writs daily produced by an adult of average 

 weight has been estimated by Ranke at 2200 (by Helmholtz at 2700), or 

 sufficient to raise the temperature of 48.4 Ibs. from the freezing to the 

 boiling-point; 1 or if converted into mechanical force, it amounts to 930,600 

 kilogram metres, which would be sufficient to raise the body of a man weigh- 

 ing 68 kilogrammes (149.6 Ibs. av.) through a vertical height of 8.5 miles. 

 This heat is expended in conduction and radiation from the body, in warm- 

 ing the air inhaled, and the water and watery vapor exhaled by the skin, 

 kidneys, and lungs, and in warming the food. Next as regards internal dy- 

 tunnical work. Professor Haughton 2 states that the work done in maintain- 

 ing the circulation and respiration may be estimated at 133 foot-tons, or 

 41,180 kilogrammetres (heart = 121 foot-tons, muscles of respiration, 11 

 foot-tons). The same authority gives as the result of numerous observations 

 on the external or daily work of various classes of laborers the mean of 

 353.75 foot-tons (109,549 kilogrammetres), which corresponds well with the 

 results obtained by Coulomb (330 foot-tons), Lamande (352 foot-tons), and 

 Playfair (346 foot-tons). The work expended in growth may be neglected 

 for the adult; and that exerted in mental operations, as already stated, can 

 only be indirectly estimated. From the foregoing calculation it would seem 

 that the entire amount of force expended in maintaining the heat of the 

 body of an adult weighing 150 Ibs. and in the performance of his internal 

 and external mechanical work is 1,044,267 kilogrammetres, of which uiue- 

 teuths is expended in maintaining the heat, and the remainder in external 

 and internal dynamical work. 3 



349. It may be shown, either from an examination of Frankland's tables, 

 or by calculating the amount of tissue decomposed to furnish the usual 

 amount of urea, carbonic acid, and water eliminated from the body, that 

 almost exactly the same amount of a million kilogrammetres of force are 

 contained in the food. Thus, on Vierordt's estimate 



120 grammes of albumen, dry, . . = 213,720 kilogrammetres. 



90 " of fnt, . . ' . . . = 345,690 " 



330 " of farinaceous compounds, . =536,910 " 



1,096,320 



The close approximation of the experimental with the calculated values is 

 of great interest. It may be objected that a very small margin is left for 

 purely mental operations ; but it must be remembered that Professor Haugh- 

 ton's estimate of 353.75 foot-tons, or 109,549 kilogrammetres, for external 

 or mechanical work, is very high, being equivalent to that required to raise 

 the body through one mile of vertical height, or to walking 20.74 miles per 

 diem, which is perhaps three times more than is usually accomplished ; and 



1 Grundziige der Physiologic, p. 476, 1868. 



2 Address delivered at the British Medical Association at Oxford, Aug. 1868. 

 Dr. Andrew Buchanan gives reasons for believing that the force of the heart (Left 

 Ventricle) does not exceed 42.3 foot-tons in the 24 hours. See Lancet, vol. ii, 1870, 

 p. <>r,r>. 



3 Prof. Haugliton, calculating the amount of heat produced from the amount of 

 Carbonic Acid gas eliminated, as shown in llanko's experiments, estimates the cal- 

 orific work at live-sixths, and the internal and external mechanical work at one-sixth 

 of the whole amount of force generated. 



