84 



Feeds and Feeding. 



68° F. than at 86° F. When he was clipped, the loss of heat from 

 his body rose from 23.6 to 37.4 Calories, an increase of 58 per ct. 

 To cover the increased heat loss at the lower temperature, an in- 

 crease in the rate of combustion or burning of fuel in the body was 

 produced thru the nervous system by the sensation of chill. 



II. Work. 



It has long been known that muscular exertion or external body 

 work greatly increases the amount of food material burned or 

 broken down in the body, but scientists have disagreed widely as to 

 whether one or all of the three classes of nutrients — protein, carbo- 

 hydrates, or fat — furnishes the energy. Liebig held that the pro- 

 tein of the muscular tissues was the only material broken down in 

 producing the voluntary and involuntary motions of the body, 

 whether of the limbs, heart, or other viscera. 



106. Waste of protein tissues during work.— That protein is not 

 an important source of body energy was shown by Professors Fick 

 and Wislicenus,^ who in 1865 ascended the Faulhorn, an Alpine 

 mountain. While ascending the mountain these investigators con- 

 sumed only non-protein food, i. e. starch, sugar, and fat, and during 

 this time they collected all the urine passed. The amount of nitro- 

 gen excreted in the urine during the trial follows : 



The table shows that only about two-thirds as much nitrogen was 

 excreted per hour during and immediately after the climb as prior 

 to it, when there was more or less residue in the system from the 

 previous meal containing protein. Had the nitrogenous tissues or 

 the muscles of the body been broken down directly in proportion to 

 the labor performed, there would have been a large increase in the 

 nitrogen excretion during and following this fatiguing work ; but 



1 Jour. Koy. Agr. Soc, 1895 ; U. S. Dept. Agr., Office of Expt. Sta., Bui. 22. 



