338 ANIMAL HEAT. 



say per diem, it is clear that we could readily calculate how 

 much heat would be produced, provided that the consumption, 

 i. e., oxidation, were complete. As regards the albuminous 

 elements of food, no such complete oxidation takes place, for 

 the elements of these compounds do not leave the organism in 

 the form of ultimate products of oxidation, but in great part 

 in the form of urea and other imperfectly oxidized organic 

 constituents of urine. The quantity of heat actually pro- 

 duced by a given weight of albumin, therefore, falls consider- 

 ably short of its heat value. In order to arrive at this 

 quantity, the deduction previously referred to must be made : 

 i. e., from the heat value of the albumin consumed, the heat 

 value of the nitrogenous excreted substances into which it is 

 transformed must be taken: the difference expresses theoreti- 

 cally the exact number of heat units actually generated by its 

 elements in their passage through the body. As regards the 

 hydro-carbons, no such deduction is necessary, so that in the 

 case of animals which feed exclusively on these compounds 

 e. g., bees the quantity of heat produced is at once obtained 

 by estimating the heat value of the food consumed. 1 



Another chemical method of estimating the rate of produc- 

 tion of heat in the body of an animal, is founded on the esti- 

 mation of the discharge of carbonic acid from the lungs and 

 skin. In carnivorous animals this method is of little value, 

 for, as we have seen, so much of the food consumed as consists 

 of albuminous compounds is incompletely oxidized, so that 

 theFe is no definite relation between the consumption of albu- 

 minous products and the amount of oxidation. In such ani- 

 mals, however, as can be fed entirely on hydro-carbons of 

 known composition, the carbonic acid gas discharged may be 

 taken as an exact index of the heat production not because 

 the quantity of heat produced, as was at first erroneously as- 

 sumed, is equal to the heat which would be disengaged by the 

 oxidation of the quantity of carbon actually contained in the 

 carbonic acid, and of the quantity of hydrogen contained in 

 the corresponding quantity of water but because in such an 

 animal the whole of the material consumed is completely oxi- 

 di/i'd ; so that the quantity of carbon discharged as carbonic 

 acid is always equal to the total quantity of the same element 

 oxidized. On this account bees, which can be fed exclusively 



1 No results can be obtained by this method unless the animal is in a 

 state of perfect nutritive equilibrium. For this reason, it can be seldom 

 applicable in the investigation of physiological or pathological questio'ns 

 relating to heat ; for, on account of the length of the periods over which 

 the determinations must necessarily extend, it gives little or no informa- 

 tion as to the variations in the production of heat, the appreciation of 

 which is practically more important than the determination of the means 

 of the quantities produced per hour or day. 



