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A MANUAL OF PHYSIOLOGY 



The heat-production during the hours of sleep, in the second night 

 period, is much less than in the waking hours of rest, and of course 

 enormously less than in the hours of work. After work the heat- 

 productiori in the period of sleep is only a little greater than after rest. 



As already indicated (p. 580), it is permissible to calculate the heat- 

 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 calories 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 calories. 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 presump- 

 tion that in Scotch prisons the total heat value supplied is not 

 excessive. From the general agreement of calculated results with 

 actual measurements we can safely conclude that most healthy adults 

 produce between 2,000 and 3,000 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. 545) indicates that the work of the world might possibly be 

 accomplished 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. 



