500 A MANUAL OF PHYSIOLOGY 



production during sleep is much less than in the ' rest ' of ordinary 

 waking life; and, on the other, continuous labour for twenty-four 

 hours at the rate of more than 30,000 kilogramme-metres per hour 

 would either be impossible, or would be associated with a greater 

 consumption of food or of tissue than corresponds to the diet on 

 which our calculation was based. During the normal eight hours 

 of sleep the heat-production of a 73 kilo man is only about 45,000 

 millicalories per hour (Helmholtz), or 360,000. Adding to this 

 2,240,000 (i6x 140,000), for the sixteen resting but waking hours, 

 we get 2,600,000 as the total heat -production of the 'resting' man. 

 Dividing the day into eight hours of work at the rate of 32,550 

 kilogramme-metres per hour (a hard day's labour), eight hours' 

 waking rest, and eight hours' sleep, we get a heat-production of 

 3,312,000 small calories in twenty-four hours, made up thus : 



Eight hours' work x 229.000 = 1,832,000 



Eight hours' ' rest * X 140,000 = 1,120,000 



Eight hours' sleep x 45,000 = 360,000 



3,312,000 



Such direct observations as have been made on man by 

 means of water or air calorimetes, or by simply immersing 

 the subject in a bath, are still open to considerable errors, 

 and the heat-production necessarily varies widely with the 

 diet. But from the general agreement of calculated results 

 with actual measurements we can safely conclude that most 

 healthy adults produce between 2,000,000 and 3,000,000 small 

 calories on a ' rest ' day, or a day of light labour, and between 

 3,000,000 and 4,000,000 on a day of hard manual work. 



Rubner has calculated from the diet the heat-production 

 of 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 2,303,000 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., 2,445,000 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 

 2,868,000 calories. The third class, composed of men who 

 work with machines and other skilled labourers, attain a 

 heat-production of 3,362,000 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 4,790,000 calories. In the fifth and last class, 



