69 



low a stall temperature also increases the amount of material required 

 for maintenance. In many cases observed, this increase was hardly 

 covered by 2 pounds of oats daily. 



ENERGY REQUIRED TO CHEW AND DIGEST FOOD. 



One of the most interesting of the lines of investigations followed 

 b}' Zuntz was the determination of the energy required to chew and 

 digest different foods. The experiments were complicated and too 

 extended to describe here except in very general terms. As has been 

 said, the respiratory quotient is a verv delicate index of the changes 

 which take place in the body, and it was found that the internal 

 muscular work expended in chewing, swallowing, and digesting food 

 could be determined by the variations in the respirator}" quotient and 

 the amount of carbon dioxid excreted when this kind of work was per- 

 formed, as compared with the amount when the animal rested. Different 

 feeding stuffs modified the respiratory quotient in different ways, and 

 it was evident that some required more labor for digestion and assimi- 

 lation than others. This is a matter of considerable importance, and it 

 is evident that if two feeding stuffs of practically the same composition 

 are digested with equal thoroughness but one requires for digestion 

 and assimilation the expenditure of more internal muscular work than 

 the other, it is really less valuable; in other words, the two may con- 

 tain the same amount of digestible nutrients, but one causes the 

 body more labor to assimilate than the other. On the basis of his 

 average figures of composition and digestibility, 2.2 pounds of hay (1 

 kilogram) furnishes 0.862 pound of total nutrients, and 2.2 pounds 

 (1 kilogram) of oats 1.353 pounds of nutrients. As regards nutri- 

 tive value, hay and oats are therefore commonly said to be to each 

 other as 400 : 600. As shown by Zuntz's experiments, 0.265 pound (115 

 grams), or 20 per cent of the total nutritive material present in 2.2 

 pounds (1 kilogram), of oats is expended in the labor of chewing and 

 digesting them. In the case of 2.2 pounds (1 kilogram) of hay, 0.448 

 pound (205 grams), or 49 per cent of the total nutritive material, is 

 required for the same purpose. Therefore hay and oats stand really in 

 the proportion of 203 :480. In other words, oats surpass hay in feed- 

 ing value two and one-half times instead of one-half times, as they are 

 ordinarily assumed to do. 



"TRUE NUTRITIVE VALUE" OF FEEDING STUFFS. 



Taking into account the internal muscular work required to chew 

 and digest foods and deducting this from the digestible nutrients pres- 

 ent in the foods, Zuntz calculated what we may call the "true nutri- 

 tive value "of a number of feeding stuffs with special reference to 

 horses. The results are shown in the foUowingf table: 



