476 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



according to the experiments of Rubner, each gram of proteid is estimated to 



yield 41D0 calorics. With those facts in view it is a simple matter to deter- 

 mine the total income of energy, should the diet he known. Thus, if the 

 diel consists of L20 grams of proteids, 90 grams of fat, and 330 of carbo- 

 hydrates, the absolute and available amounts of energy ingested are — 



Grams. Calories. Calories. 



Proteids 120 x .->77s 693,3ti0 



Fats 90 x 9312 837,080 



Carbohydrates 330 x 411G 1, 358,28 



2,888,720 



Dedmt the proteid energy in 40 grams of urea, 40x2523= 100,92 



Total daily heat-production 2,787,800 



This is assuming that the entire quantity of proteids, fats, and carbohydrates 

 is digested, absorbed and ultimately broken down into 0O 2 , H 2 0, and urea. 

 This assumption, however, is not justified by facts, since we know, for instance, 

 that more or less food escapes digestion. Moreover, the calorimetrical values, 

 at hast for proteids, are probably too high. In practice, therefore, it is nec- 

 essary to ascertain from the excreta of the animal (see section on Nutrition) 

 just how much of the ingested food has been absorbed and completely 

 or partially destroyed in the body. 



Calorimetric investigations also afford us indirect information as to the 

 income of heat by showing the quantities of heat produced and dissipated. 

 Such data are of much value, since it is evident that should the energy of the 

 body be maintained in a condition of equilibrium from day to day, and should 

 the energy resulting from the transformation of potential energy be manifested 

 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-time-) 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 exec— of energy be ingested, as in excessive 

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

 duetion, because >oine 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 calorimetric method see p. 482.) The results 

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

 total income of available energy i> 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 Yierordt that about — 



