UNIV. OF N. H. AGR. EXPERIMENT STATION 



[Bulletin 240 



In the splitting up of the oxidized material that follows, a definite amount 

 of heat is produced, and a definite amount of carbon dioxide is set free. 

 This latter forms a waste product, which in turn is largely discharged 

 through the lungs. The details of this process will not be explained here, 

 but it is a fact that oxidation is a chemical reaction and is thus char- 

 acterized by a degree of exactness which may be considered absolute. 

 The rate of production of active energy accordingly has a definite de- 

 pendence on the rate of lung ventilation, i.e., on the amount of oxygen 

 consumed and on the amount of carbon dioxide expelled. Measurements 

 of oxygen intake and carbon-dioxide output, therefore, give an accurate 

 picture of the rate of energy metabolism taking place within the body at 

 any given time. Hence the terms "respiration chamber" and "respira- 

 tion apparatus" have been accepted to designate the equipment used to 

 measure this respiratory exchange and thus indirectly to measure the 

 energy transformed. 



By indirect calorimetry it is possible not only to measure the amount of 

 material oxidized or burned in the body, but also to determine the char- 

 acter of the material so used. Energy -yielding material, as it is ulti- 

 mately usable for oxidation, occurs in three forms, viz., carbohydrate, fat, 

 and protein. These differ in the amount of oxygen they require for 

 oxidation and also in the amount of resulting carbon dioxide, as is shown 

 in Table I. 



Table I — Oxygen consumed, carbon dioxide and heat produced per gram of food substance as oxidized in the 

 body, and the respiratory quotient, or ratio of carbon dioxide to oxygen ' 



1 Biological tables have been compiled on the basis of these values, whereby the energy metabolized by the 

 animal can be readily computed from the amount of gaseous exchange and from the volume ratio of the 

 gases. See Carpenter, T. M., Carnegie Inst. Wash. Pub. No. 303A, 1924, Tables 13 and 14, pp. 104 and 105. 



The determination of the energy metabolism of non-ruminant animals, 

 particularly humans, by methods based on measurement of the exchange 

 of these two gases, oxygen and carbon dioxide, has now attained universal 

 acceptance, and the technique has been highly standardized — so much so 

 that other methods would now be considered impractical, inefficient, and 

 unscientific. 



Unfortunately the practical application of indirect calorimetry in the 

 measurement of the energy values of feeds and the energy require- 

 ments of cattle has not received an equally unqualified acceptance. The 

 progress made in studying energy transformations has been more rapid 

 with humans than with animals, due in part to the differences in experi- 

 mental objective and in part to the fact that the use of complex apparatus 

 heretofore necessary for this purpose has been deemed justified in the 

 case of humans but has not been considered justified in the case of large 

 farm animals. 



In metabolism studies with humans the needs of the individual and the 

 efficiency of the diet to meet these needs are important primarily as they 



