ENERGY USED IN DIGESTION 123 



per cent. ; while in the case of wheat straw the con- 

 sumption of energy while the food is passing through 

 the animal is actually greater than the energy finally 

 obtained ttom the digested straw.^ Zuntz reckons that 

 9 per cent, of the digested food is generally to be de- 

 ducted for digestion work, but that each gram of fibre 

 in the food, whether digested or not, consumes energy 

 equal to 2*6 Calories for its mastication and passage 

 through the alimentary canal. We must bear in mind 

 that the excessive wastefulness of fibrous foods shown 

 in these investigations on the horse is not true to an 

 equal extent in the case of ruminant animals. With 

 them the fibre is softened in the paunch before mas- 

 tication takes place, and the digestion of the fibre has 

 made some progress before the intestines are reached ; 

 moreover, the fasces are far more watery in character, 

 and should pass through the system with less effort. 

 The proportion of fibre digested by the ox and sheep 

 is also considerably higher than the proportion digested 

 by the horse (see p. 146). The general indications of 

 these valuable experiments are, however, very plain, 

 and must apply more or less to every animal. 



Foods have a very different value for different pur- 

 poses. We have already seen that the value of a food 

 for the production of heat is simply the fuel value of 

 the digested matter minus the fuel value of the urine 



* More information is required as to the utilisation of straw by the 

 horse. Miintz fed a horse with wheat straw alone from November 19 

 to January 20, when the horse died thoroughly exhausted. The horse 

 digested during December 375 lbs. of organic matter for 1,000 lbs. of 

 straw supplied. This is double the amount assumed as digested in 

 Zuntz's table, and would leave a small balance for the use of the 

 animal. 



