METABOLISM 11 



in the production of the outward task and how much in 

 increased internal work, but one may say approximately 

 that only about one-fifth should be put down to the work 

 itself, and four-fifths to internal expenditure. The human 

 body is therefore rather more economical than the best 

 steam-engine, which gives about 15 per cent, of its total 

 discharge of energy as work, and the rest as heat. 



Practice, however, is of great importance in this con- 

 nection, for a man who is skilled in the performance of 

 any special piece of work certainly does it more economic- 

 ally and with relatively less increase of internal work 

 than one who is unskilled. One illustration will make 

 this clear. It was found by Hueppe, in comparing the 

 expenditure of energy by an untrained town-dweller and 

 an Alpine carrier in climbing, that in the course of a 

 six hours' ascent the former expended 449 Calories in 

 work and 1,000 Calories in heat, whereas the latter 

 expended 884 Calories in work, and only 565 in heat. 



Fatigue, pain, overheating of the body, and being in 

 bad health or ' out of condition,' are also all of them 

 factors which increase the ' expense ' of work. A man, 

 for instance, who is tired, footsore, and very hot, will 

 expend more energy in walking a given distance than is 

 really necessary to carry his body over the same space 

 under better conditions. 



It must not be assumed from all this that human 

 labour is necessarily cheaper than that of a steam- 

 engine. Quite the contrary, of course, is the case. If, 

 for instance, a labourer works five days a week and earns 

 20s., of which he spends 5s. upon food, and has a total 

 daily intake of energy of 3,000 Calories, of which 500 



