THE NITROGEN-FREE EXTRACT OF FEEDING STUFFS. 657 



In fact, Henneberg- and oMiers liave divided tlie crude fiber deter- 

 mined by analysis into two ])arts, tlio digestible crude fiber and the 

 undigestible crude fiber; and special analytical studies have shown that 

 the digestible portion of the crude fiber has the composition of cellu- 

 lose (C(;II,oOr,), or 44.44 per cent of carbon, 0.17 per cent of hydrogen, 

 and 40..3S per cent of oxygen. 



In other words, more or less of the cellulose in the crude fiber is dis- 

 solved in the animal body, and it is evident that this dissolved cellu- 

 lose in some way takes part in nutrition, and can not be disregarded 

 in investigations of this character. The matter has been much dis- 

 cussed, and the question as to whether or not this digested cellulose 

 acts in the same "way in nutrition as the nitrogen-free extract has been 

 answered in very different ways. 



Since the crude fiber which is dissolved in the digestive tract has 

 been found by Ilenneberg and other chemists (notably Konig) to have 

 the composition of cellulose, a carbohydrate, and since the cai-bohy- 

 drates comprise the i)rincipal part of the nitrogen-free extract, it 

 would seem to follow that the digested crude fiber would have the 

 same nutritive effect as the digested nitrogen free extract. This con- 

 clusion appears to the writer to be at least ai)proximately correct. 

 But this belief is not shared by all. 



The function of the food is not only to furnish materials to repair 

 the waste and to maintain tlie body or produce growth or fat, but also 

 to furnish heat and energy. For the production of heat and energy 

 the carbohydrates (and consequently the nitrogen Irec extract) are 

 well adapted; and for a proper knowledge of their value in this 

 respect, the desirability of knowing the heats of combustion of the 

 carbohydrates and other constituents of the nitrogen-free extract is 

 recognized on all sides. The heat production is the same when a sub- 

 stance is burned rapidly and with a fiame in oxygen as when it is 

 slowly changed by the respiration of the animal into carbon dioxid 

 and water. 



Frankland, Berthelot, and Stohmann especially, have made large 

 uunjbers of determinations of the heats of combustion of various sub- 

 stances,^ and from the fuel value calculated for 1 gm. of this or that 

 feeding stuff a conclusion can be drawn as to its value in nutrition. 



In the production of heat by the oxidation of organic niattcr, it is 

 immaterial whether or not in the change to carbon dioxid and water 

 intermediate i)roducts are formed which in turn are oxidized to carbon 

 dioxid. But it is by no means immaterial when intermediate products 

 are formed which prevent a complete oxidation. Tliis is the case with a 

 in'oduct which often results from the decomposition of the carbohydrates, 

 namely, marsh gas, or metlian (CH4), which is formed in large quanti- 

 ties in the stomachs of ruminants and is given ott' into the air unoxi- 

 dized, so that the heat of its carbon is lost. As mentioned above, a 

 part of the cellulose is dissolved in the ])rocess of digestion as a result 



'U. S. Dept. Ajj;r., Ofiic(^ of Experiment Stations Hul. 21. 



