INVESTIGATIONS < >N THE METABOLISM OF MILCH COWS. 907 



For each 100 gm. of digested crude fiber completely oxidized in the 

 animal body 149.99 gm. (110.19+33.5 = 149.99) of carbon dioxid (equal 

 to 76.28 liters) is produced, and 98.1 gm. of oxygen (equal to 68.6 

 liters) is consumed from the air. The respiratory quotient is therefore 



68.6 - 1 - 11 - 



The fuel value of the cleavage products of the crude fiber can also 

 be calculated from the oxygen utilized and the carbon dioxid pro- 

 duced. One hundred grains of crude fiber has a fuel value of 118.5 

 calories; 1.7 gm. of methan would yield 02.7 calories (1.7x13.341 [fuel 

 value of 1 gin.] =62.7); 0.2 gm. of hydrogen would furnish 0.9 calories 

 (0.2x34.0 [fuel value of 1 gm.]=0.9; deducting the sum of G2.7 and 

 6.9 from 418.5 leaves in round numbers 349 calories. A total of 68.6 

 liters of oxygen would be used; that is, each liter of oxygen utilized 

 for the combustion of digestible crude fiber produces 5.087 calories 



( pg-g = 5.087 ). A correction should, however, be introduced for the 



33.5 gm. of carbon dioxid and about 48 calories produced by fermenta- 

 tion. Under certain conditions this heat is as available for the body 

 as that produced by the oxidation of materials in the tissues. Further, 

 according to the investigations of Munk and Mallerve sodium butyrate 

 and sodium acetate may be burned in the body, but the metabolism is 

 also increased so that at best only four-fifths of their nutritive value is 

 available. After deducting the 48 calories due to fermentation from 

 the 349 calories per kilogram of digestible crude fiber mentioned above, 

 there remain 301 calories. Assuming that only four-fifths of this is 

 available, 100 gm. of digestible crude fiber yields for the body 210.8 

 calories. Using this value, 1 liter of oxygen from the inspired air 

 would produce 3.51 calories (240.8-^- <i8.0 = 3.51). 



Energy is required for taking food into the mouth, chewing it, and 

 for chewing the cud, and for all the processes of digestion. More or 

 less energy is also required for the secretion of saliva and other digest- 

 ive juices, and for taking up the digested material into the blood and 

 lymph. The food must be moved through the intestinal tract, and 

 finally the undigested matter must be excreted. Further, the labor of 

 digestion causes increased activity of the heart and lungs. The result- 

 ant of all the energy expended is heat, and only a part of this heat is 

 necessary for maintaining the" body temperature. It is probable that 

 when milch cows are fed an abundant diet so much heat is produced 

 by the labor of digestion that a portion is radiated from the body 

 unused. 



It is plain, then, that a deduction must always be made from the 

 total energy of a maintenance ration to cover the labor of digestion. 

 The labor of chewing and digesting increases with increased amounts 

 of crude fiber in the food. This has been shown by many experiments 

 with cattle and horses. Zuntz and the writer found that with a horse 

 the labor of chewing and digesting amounted to 200 calories per 100 



