684 ANIMAL HEAT 



agreement between the potential energy of the food and the kinetic 

 energy into which it is transformed in the body both during rest 

 and during work. This kinetic energy is represented by the heat 

 "given off plus the heat-equivalent of any mechanical work done 

 (Atwater). In other words, the food, whether it is burned in a 

 calorimeter to simple end-products like carbon dioxide and water, 

 or more slowly oxidized in the body, yields the same amount of 

 heat, provided always that in both cases it is entirely consumed, and 

 that no work is transferred to the outside. In the body the com- 

 bustion of carbo-hydrates and fats is complete; but the nitrogenous 

 residues of the proteins urea, uric acid, etc. can be further 

 oxidized, and the remnant of energy which they yield must be 

 taken into account in any calculation of the total heat-production 

 founded on the heat of combustion of the food substances. Froni 

 careful experiments, it has been found that a gramme of dry protein 

 (egg-albumin), when burned in a calorimeter, yields 5735 calories 

 of heat, a gramme of dextrose 3742, and a gramme of animal fat 

 9-500 calories (Stohmann). 



Calories. 



Heat-equivalent of I gramme of albumin - 5 -735 



Albumin (minus urea produced from it) - - 4*949 



Cane-sugar - - 3 -95 5 



Kreatin (water-free) 4* 2 75 



Starch - - 4-182 



In applying such results to the calculation of the heat-production of 

 the body, it is not sufficient to deduct from the heat of combustion of 

 the proteins the heat which the residual urea would yield if fully 

 oxidized. For other incompletely oxidized products arise from pro- 

 teins when consumed in the body, and. Rubner has shown, by actually 

 determining the heat of combustion of the urine and faeces, that the 

 real equivalent of a gramme of albumin is at most only 4-420 calories. 

 The heat-equivalent of our less liberal specimen diet (p. 625) will be 

 approximately : 



Calories. 



Protein, 95 grammes x 4-420 419-9 



Fat, 80 grammes x 9-500 760-0 



Carbo-hydrate (reckoned as 



dextrose), 320 grammes x 3*742 1,197-4 



2,377'3 



The heat-equivalent of the more generous specimen diet (p. 627) would 

 be 2,878 calories. 



But this is the diet of a man doing a fair day's work, and to get the 

 quantity of energy which actually appears as heat, the heat-equivalent 

 of the mechanical work performed must be deducted. A fair day's 

 work is about 150,000 kilogramme-metres that is, an amount equal 

 to the raising of 150,000 kilogrammes to the height of a metre. Now, 

 a kilogramme-degree or calorie of heat is equivalent to 425-5 kilo- 

 gramme-metres of work, and a kilogramme-metre to - - calorie. 



4 2 5'5 



The heat-equivalent of the day's work is, therefore, 150,000 x 



4 2 5'5 

 352 calories. Deducting this from the heat-equivalent of the food. 



