68 



Feeds and Feeding. 



air engine, or can even be considered its direct source/ since the 

 necessary conditions of alternate heating and cooling of the whole 

 or a part do not hold good in the animal body, and make a com- 

 parison between the two impossible The increased 



production of heat during work and the increased respiration are 

 but secondary effects, the result of work, and can by no means 

 be regarded as its primary or direct cause. The increased heat 

 produced in work is dissipated in evaporation from the body and 

 by greater heat radiation, and is eventually reduced again to the 

 normal.' 7 



96. Food requirements for work vary. Wolff further writes: 1 

 "The food required to produce work varies with the form of 

 muscular activity or the work done. Katzenstein, for instance, 

 found that work done by men turning a wheel with the arms 

 produced a greater expenditure of material in the body than the 

 same work done with the legs. The volume of oxygen used per 

 kilogram-meter of work done with hand-labor amounted to 1.96 

 cubic centimeters, but when the work was done with the legs, 

 only from 1.19 to 1.51 cubic centimeters." 



Further, the degree of practice in a particular kind of work 

 influences the expenditure of material in the body, as Gruber 

 found by experiments on himself. The carbonic acid produced 

 every twenty minutes amounted to the following: 



Zuntz and Lehmann obtained similar results in their experi- 

 ments on the horse. "It can be deduced from the total experi- 

 mental results that no constant relationship can be set up between 

 the production of work and consumption of food; the entire 

 organization of an animal, its individual and variable peculiarities 

 and condition, etc., create great differences in the economical 



1 Farm Foods, pp. 84, 85. 



