584 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



solely in the form of heat, it follows that the mean daily heat-production and 

 income of available energy must balance. But it cannot be considered that this 

 balance is maintained at a constant standard from hour to hour, nor from day 

 to day ; on the contrary, the fluctuations are undoubtedly considerable, as is 

 obvious by the fact that we are continually expending energy and only periodi- 

 cally (at meal-times) acquiring energy. During fasting there is absolutely no 

 income of energy, yet the output of heat may be subnormal, normal, or hyper- 

 normal ; on the other hand, if an excess of energy be ingested, as in excessive 

 eating, it is not by any means implied that there is a similar excess in heat-pro- 

 duction, because some of the food ingested may be lost as undigested food or as 

 partially oxidized excrementitious matters, or may be stored in the body in the 

 form of carbohydrate, fat, or proteid ; nor does an excess of heat-production 

 imply an excess of income of energy, because the stored-up energy may be 

 drawn upon. (For results of the calorinietric method see p. 589.) The results 

 of the various methods are in close accord, and indicate that in the adult the 

 total income of available energy is about 2,500,000 calories. 



Expenditure of Heat. Assuming that the energy of the organism is 

 expended in the form of heat, and that the total income of available energy is 

 2,500,000 calories, it has been estimated by Vierordt that about 



1.8 per cent, is lost in the urine and feces 47,500 calories. 



3.5 " " " expired air 84,500 " 



7.2 " " " evaporation of water from the lungs 182,120 " 



14.5 " " " " " " skin. 364,120 " 



73.0 " " " radiation and conduction from skin 1,791,820 " 



2,500,000 calories. 



Therefore, about 87.5 per cent, is lost by the skin, 10.7 per cent, by the lungs, 

 and 1.8 per cent, in the urine and feces. 



C. HEAT-PRODUCTION AND HEAT-DISSIPATION. 



Calorimetry. The intensity of heat of any substance is measured by means 

 of a thermometer or thermopile ; the quantity of heat present is estimated by 

 the weight, the specific heat, and the mean temperature of the body ; the quan- 

 tity of heat dissipated is measured by the calorimeter ; and the quantity of 

 heat produced is determined by the quantity dissipated plus any addition of 

 heat to that of the body or minus any that is lost (p. 588). The calorie, or heat 

 unit, is the quantity of heat that is necessary to raise the temperature of one 

 gram of water 1 C. ; the mechanical unit, or grammeter, is the quantity of 

 energy required to raise one gram a height of one meter, and is equal to 424.5 

 calories ; a kilocalorie or kilogramdegree is equal to 1000 calories, and a kilo- 

 grammeter to 1000 grammeters. By specific heat is meant the quantity of heat 

 required to raise the temperature of any substance 1 C., this quantity varying 

 considerably for -different substances. If water be taken as 1, as a standard of 

 comparison, the specific heat of the animal body may be regarded as being 

 about 0.8 ; in other words, 0.8 of the quantity of heat will be required to heat 

 the same weight of the animal body as to heat the water. Knowing the weight, 



