318 



THE ANIMAL AS A PRIME MOVER. 



the food, or less, might be expected to be wholly wasted. Very nearly 

 this efficiency was attained by the same individual during five days of 

 recuperation after a five days' walk of 317.5 miles. 



The food of the human prime motor has been seen to yield from 

 about 2,500 calories, L0,000 British thermal units, 7,800,000 foot- pounds, 

 nearly, when doing - little or no work, up to 4,000 calories, 16,000 Brit- 

 ish thermal units, 12,500,000 foot-pounds, nearly, when doing a maxi- 

 mum day's work. This would seem to indicate that the internal work 

 of brain, nerves, muscles, and other organs of work and thought and 

 heat production must be about three times the total external work of 

 a working day, and this, in turn, would again make the efficiency of 

 the vital machine one-quarter, 25 per cent, corresponding once more to 

 the maximum given by Hirns's. direct experiments. 



Reviewing what has been thus far collated, it will probably be 

 admitted that the following may be taken as a fair estimate of the 

 efficiency and energy distribution of the average representative human 

 prime motor, assuming 10,000,000 foot-pounds supplied and 85 per cent 

 of the food to be digested : 



Hie animal machine— Receipts and expenditurex — Efficiencies. 



Received food-content. 



Energy 

 utilized. 



Per cent of energy 

 available. 





10,000,000 

 1,500,000 



8, 500, 000 



85 100 



Loss unassimilated 











2, 000, 000 



o, 700, 000 



500, 000 



2, 300, 000 



23. 5 | 20 

 43. 5 ; 37 

 5.9 5 

 27. 1 23 

 15 







Thought-energy 



Internal work other than friction 



Wastes by nonassimilation, as above .. 



Total 











8, 500, 000 



100 100 



'Dalton. 



Where the machine is a thought-machine, and not primarily a prime 

 motor, the efficiency may be quite different, as will be seen later. 



The wasted energy of the vital machine, when considered merely as a 

 work producer in the ordinary sense of that term, consists of the 

 various internal energies expended in the operation of the machine, 

 the misapplied mechanical energy of the twenty-four hours, and the 

 heat radiated and conducted from the body and exhaled from the lungs. 

 Could all these wastes be suppressed, the efficiency of the machine 

 would be unity as a prime motor. Precisely what are these energies 

 and their respective amounts is, as yet, unknown; their aggregate has 

 been seen to be 80 per cent. To what extent either or all may be sup- 

 pressed, as our knowledge of the machine enables us to employ it more 

 and more intelligently, no one can yet say, except that it is known that 

 the losses of heat from the exterior of the body may be kept down to a 



