908 EXPERIMENT STATION RECORD. 



gm. of crude liber in the food. Values for milch cows are necessarily 

 somewhat different, since the processes of digestion in ruminants and 

 horses are dissimilar. In the case of a horse, protein, fat, and carbo- 

 hydrates are acted upon by the digestive juices and absorbed in the 

 stomach and small intestine. The cellulose and materials which have 

 escaped digestion, because the walls of the cells in which they are 

 inclosed have not been broken, finally reach that portion of the intes- 

 tinal tract where fermentation takes place. The fermentation renders 

 the crude fiber soluble, and further, when the cell walls are thus 

 destroyed the nutrients which escaped digestion earlier can be reached 

 by the digestive juices and absorbed. The act of moving the crude 

 fiber through the long intestine to the point where fermentation takes 

 place requires an expenditure of energy which may safely be assumed 

 to reach 2.65 calories per gram of crude fiber in the food. 



In the case of ruminants the food is retained for a long time in the 

 first stomach and undergoes very active fermentation. This renders a 

 large portion soluble and diminishes the amount of crude fiber, so that 

 only a portion of the crude liber must pass through the whole intestinal 

 tract, the exact amount of which is not known. At all events, this 

 step in digestion requires the expenditure of less energy than in the 

 case of horses. On the other hand, chewing the end requires a large 

 amount of energy; so that it is not impossible that the total labor of 

 digestion is fully as great in ruminants as in horses. 



Cattle digest in round numbers CO per cent of the crude fiber con- 

 sumed. Using Kiihn's data, Kellner has calculated, that owing to fer- 

 mentation 10 per cent of the digestible carbon is excreted in the form 

 of hydrocarbons. Thus, of 100 gm. of crude fiber fed, GO gm. is digest- 

 ible, and 30 per eent, or 21. gm., undergoes fermentation. This has a 



fuel value of 52 calories ( -jt^c X 21.6=52 J. The total energy of the 



38.1 gm. (60—21.6=38.1) of digestible crude fiber remaining is available. 

 Since this is 1.18 calories per gram, the total would be 160 calories. 

 In other words, 100 gm. of crude fiber in the food, of which 60 gm. is 

 digestible, furnishes the body 212 calories (52 + 160 = 212). Since a 

 horse requires 265 calories, this amount would be insufficient, infor- 

 mation is lacking for ruminants, especially milch cows, and special 

 respiration experiments will need to be made in which rations containing 

 large and small amounts of crude fiber are fed before statements such 

 as the foregoing can be made with certainty. From what has been said 

 it is probable that the labor of chewing and digesting food is less with 

 ruminants than with horses, so that possibly the cleavage of crude 

 fiber furnishes an amount of energy sufficient for digesting it. 



The total labor of digesting fat in the case of man and dogs is not 

 great. For protein and carbohydrates it is somewhat greater than for 

 fat, amounting, according to the investigations of Magnus-Levy, aside 

 from the labor of chewing, to about 9 per cent of the total energy of 



