256 Agricultural Chemistry. 



be considoivd alone in Ibis connection. The source of the energy 

 evolved during labor and appearing as extra work and heat must 

 come from the oxidation of food. If work is to be performed 

 and at the same time body weight remain constant, the quantity 

 of food must be increased. 



It was supposed at one time that muscular effort was produced 

 by the oxidation of the nitrogenous constituents of the muscle, 

 and that a ration very rich in protein was necessary, if hard work 

 was to be maintained. This idea is now known to be erroneous. 

 Men have climbed mountains and measured the excretion of urea 

 (the principal nitrogenous constituent of the urine) during such 

 severe exercise. There was no important increase in its produc- 

 tion under such conditions. Increased work increases the excre- 

 tion of carbon dioxide but not of nitrogen. In other words, the 

 carbohydrates and fats are largely the fuel materials that furnish 

 energy for mechanical purposes. 



Zuntz has determined the quantity of food which a horse needs 

 in order to perform work under varying conditions. "A horse 

 weighing with harness 1144 pounds, will require 1.33 pounds of 

 available food to walk 10 miles at 2% miles per hour ; 1.69 pounds 

 when walking the same distance at a speed of 3 1/3 miles per 

 hour ; and 2.53 pounds when trotting the same distance at 7 miles 

 an hour. ' ' This is important knowledge on the influence of speed 

 upon the food requirement in a unit of time. 



The pace of the animal is another important factor. Grandean 

 and Leclerc kept a horse in good condition, walking 12% miles 

 a day with a daily ration of 19.4 pounds of hay, but when thf 

 same distance was done trotting, 24 pounds was insufficient. A 

 horse walking the above distance and hauling^ a load (equivaleul 

 in additional work to 1943 foot-tons) was maintained by a ration 

 of 26.4 pounds of hay ; but when the same work was done trotting, 

 a daily ration of 32.6 pounds of hay, which was all it would eat 

 was insufficient to maintain weight. Trotting or galloping in- 

 volves additional internal work; the animal also lifts its own 

 weight at each step, which only appears as heat as it falls bacfc 



