VARIATIONS IN HEAT-PRODUCTION. 447 



The albumin, however, is only oxidised to the stage of urea, hence the heat- 

 units of urea must be deducted from 4,998, which gives 4,263 heat-units obtainable 

 from 1 grin, albumin. When we know the number of grammes consumed, a 

 simple multiplication gives the number of heat-units. 



The heat-units will vary, of course, with the nature of the food. J. Ranke 

 gives the following: 



With animal diet, 2,779,524 heat-units. 



food free from N, .... 2,059,506 



,, mixed diet, 2,200,000 



,, during hunger, .... 2,012,816 ,, 



216, Variations in Heat-production, 



According to Helmholtz, an adult weighing 82 kilos, produces 2,732,000 calories 

 in 24 hours. 



(I.) Influence of the body-weight. Accepting the above number, Immermann has 

 given the following formula for the heat-production in living tissues: 



(where W = 2,732,000; P = 82 kilos. [W : yy = 144,75]; p =body-weight of the 

 person to be investigated, and w represents the heat-production which is required. ) 

 It is highly desirable that W : *^p~2 ( = m) was ascertained as a mean from a 

 large number of observations, then the heat production for any body-weight p 

 would be 



w = m v'p 2 . 



(2.) Age and Sex. The heat-production is less in infancy and in old age, and it 

 is less in proportion in the female than in the male. 



(3.) Daily Variation. The heat-production shows variations in 24 hours corre- 

 sponding with the temperature of the body (213, 4). 



(4.) The heat-production is greater in the waking condition, during physical and 

 mental exertion, and during digestion, than in the opposite conditions. 



217. Relation of Heat-production to the 

 Work of the Body. 



The potential energy supplied to the body may be transformed into 

 heat and potential energy (see Introduction). In the passive condition, 

 almost all the potential energy is changed into heat ; the workman, how- 

 ever, transforms potential energy into work mechanical work in 

 addition to heat. These two may be compared by using an equivalent 

 measurement, thus, 1 heat-unit (energy required to raise 1 gramme of 

 water 1C.)= 425*5 gramme-metres. 



The following example may serve to illustrate the relation between heat- 

 production and the production of work: Suppose a small steam-engine to be placed 

 within a capacious calorimeter, and a certain quantity of coal to be burned, then 

 as long as the engine does not perform any mechanical work, heat alone is produced 

 by the burning of the coal. Let this amount of heat be estimated, and a second 

 experiment made by burning the same amount of coal, but allow the engine to dq 



