486 Journal of Agricultural Research voi. iii, no. e 



For finer materials like chaff, presumably requiring a less expenditure for 

 mastication, 0.70 Calorie per gram of total crude fiber is deducted. For 

 green forage containing 16 per cent or more of crude fiber the same 

 deduction is made as for dry forage and for that containing 4 per cent or 

 less of cnide fiber, the same as for chaff, while between these limits a 

 sliding scale is used (24, 1905, p. 593-594). For concentrates a factor 

 (Wertigkeit) is estimated from the direct results on similar feeds by 

 which the energy value computed from the digestible nutrients is multi- 

 plied to obtain the actual value. 



The method of computation just outlined is not only somewhat com- 

 plicated but is essentially based on the older view which regarded the 

 feed in the light of a source of matter to the body. The digestible pro- 

 tein, carbohydrates, and fat are still the basis of the calculation, although 

 certain more or less empirical corrections are applied to their computed 

 effects. The energy content of a feeding stuff, however, is just as definite 

 a quantity as its content of protein, carbohydrates, or fats, and it is 

 entirely possible to trace the distribution of that energy in the body 

 quite independently of any knowledge of the chemical composition of 

 the materials. Not only so, but we believe that in discussing energy 

 values there are distinct advantages as regards simplicity, and perhaps 

 also as regards accuracy, in cutting loose entirely from the conventional 

 data regarding chemical composition and digestion coefficients, as has 

 been done in reporting our experiments on preceding pages, and in dealing 

 directjy with quantities of energy. 



In making this statement we would by no means be understood to 

 stigmatize comparisons based on chemical methods as either valueless 

 or superfluous. The problems of nutrition are too complex and tgo 

 difficult for us to refuse any light that can be thrown on them by any 

 method, and the energy relations touch only one phase of them. The 

 point is that in whatever degree their energetic aspects can be separated 

 from their chemical aspects, to that extent we possess two independent 

 methods of approach to them. 



COMPUTATION OF NET ENERGY VALUES 



The computation from the results of metabolism experiments or from 

 the data of ordinary feeding tables in the manner just indicated of the 

 net energy value of a feeding stuff which has not been the subject of 

 direct experimental investigation with the respiration apparatus or 

 calorimeter may be made a comparatively simple matter. The net energy 

 value is equal to the metabolizable energy minus the energy lost as heat. 

 It was shown on pages 450-45 1 that the metabolizable energy may be deter- 

 mined experimentally without special difficulty and with a good degree 

 of accuracy bj' means of the ordinary metabolism experiment in which 

 the energy of the feed, feces, and urine is directly determined and that 



