INCOME AND EXPENDITURE OF ENERGY 



661 



production from the diet, and Rubner has done this for various classes 

 of men, reducing everything to the standard of a body-weight of 

 67 kilos. The fasting man, of 67 kilos body-weight, produces 2,303 calo- 

 ries in the twenty-four hours. The class of brain-workers, represented 

 by physicians and officials, produce only a little more heat than the 

 fasting man, viz., 2,445 calories. The second class, represented by 

 soldiers (presumably in time of peace) and day-labourers (probably of 

 a cautious and conservative type), work up to 2,868 calories. The 

 third class, composed of men who work with machines and other skilled 

 labourers, attain a heat-production of 3,362 calories. The fourth class, 

 typified by miners (who are engaged, usually by the piece and not by 

 the day, in severe and exhausting toil), produce as much as 4,790 calo- 

 ries. In the fifth and last class, represented by lumberers and other 

 out-of-door labourers (who, in addition to excessive exertion, have 

 often to face intense cold), the heat-production rises to 5,360 calories. 

 The diet of ordinary prisoners in Scotland, doing light work, chiefly of 

 a sedentary character, was found to correspond to 3,115, and that of 

 convicts on ' hard labour ' to 3,707 calories. It is a fair presumption 

 that in Scotch prisons the total heat value supplied is not excessive. 

 From the general agreement of calculated results with actual measure- 

 ments we can safely conclude that most healthy adults produce between 

 2,000 and 3,000 large calories (35 to 40 per kilo of body-weight] on a ' rest' 

 day, or a day of light labour, and between 3,000 and 4,000 (45 to 60 per 

 kilo of body-weight] on a day of hard manual work. 



What has been already said in connection with standard dietaries 

 (p. 612) indicates that the work of the world might possibly be accom- 

 plished as well with a smaller transformation of energy in the human 

 machine, at least in the more prosperous countries, and that in the 

 body, as in an engine, more careful ' stoking ' might result in a saving 

 of fuel. It is extremely improbable, however, that any argument of 

 this sort will have much effect upon the deep-rooted dietetic habits of 

 mankind. 



In any case it must be carefully remembered that the question of 

 the minimum amount of protein necessary in a permanent diet is 

 quite distinct from the question of the minimum heat value of the diet 

 for a man of given body-weight doing a definite amount of work under 

 definite conditions. Whether the protein allowance be scanty or liberal, 

 the total heat value cannot be permanently reduced below a certain 

 minimum depending on the work done, the climate, and other conditions. 



