694 PHYSIOLOGY OF THE DOMESTIC ANIMALS 



degree of oxidation occurring in the animal body. This factor has been 

 estimated as corresponding to five heat-units. With these data the 

 amount of heat developed in twenty-four hours may be readily calculated; 

 Thus, taking the example given, by Fick, the 'income of the body was 

 represented in round numbers by one hundred and twenty grammes of 

 fat, two hundred and sixty-three grammes of carbohydrates, and one 

 hundred and seventeen grammes of albumen, with the excretion of 

 thirty-nine grammes of urea. The combustion of one gramme of fat is 

 represented by the development of nine and six-tenths heat-units, and, as 

 already seen, one gramme of carbohydrates by four heat-units, and one 

 gramme of albumen by five heat-units. The total amount of heat, there- 

 fore, developed is represented by 120 X 9.6 + 263 X 4 -f 117 X 5, or, in 

 round numbers, two thousand eight hundred heat-units. The confirma- 

 tion of these figures and their influence in maintaining the heat of the 

 animal body is determined by calorimetric experiments. To accomplish 

 such an experiment, first, the tissue change in twenty-four hours must be 

 calculated ; seoond, tiie amount of heat liberated by the body in that 

 time ; third, the average temperature of the animal body at the com- 

 mencement and end of the experiment; and, fourth, the average heat 

 capacity of the body. As a rule, the difference between the body tem- 

 perature at the commencement and end of such experiments is so slight 

 as not to deserve attention, and the amount of heat set free in twenty- 

 four hours may be regarded as indicating the amount of heat developed 

 in the body. 



Such experiments do not, however, serve with absolute accuracy to 

 confirm the theoretical figures deduced from the co-efficient of heat 

 production represented above as belonging to the different food-stuffs. 

 In nearly all cases there is an apparent loss of heat over what should be 

 expected from these data. It is to be recollected, in the explanation of 

 this discrepancy, that the energy set free in such oxidations may take 

 on the form either of heat or of mechanical work. In the animal body 

 all these sources of loss of energy occur. All forms of muscular move- 

 ment are accompanied by liberation of energy, and a continual loss of 

 heat is taking place through radiation from the surface of the body, by 

 conduction, by the evaporation from the skin and mucous surfaces, and 

 by the warming of the ingesta. The amount of heat dissipated by the 

 animal body in a condition of health is in close dependence upon the 

 amount produced, upon the difference in temperature between the animal 

 body and the surrounding medium, and especially upon the relationship 

 between the external surface of the body and the body weight. Thus, 

 small animals for each kilogramme of the body weight set free more heat 

 than large animals. It has been estimated that for each kilogramme of 

 body weight the horse in each hour sets free two and one-tenth heat- 



