66 



Feeds and Feeding. 



nitrogen excreted per hour during each of the periods, as given 

 in the last column of the table, bring the main results more clearly 

 to view. It is seen that, on the average, only about two-thirds 

 as much nitrogen was excreted per hour during and after the 

 ascent as prior to it, when there would be more or less residue in 

 the system from the last albuminous meal." 



Had the nitrogenous tissues of the body been broken down 

 directly in proportion to the labor performed, there would have 

 been a large increase of nitrogen in the urea of these persons dur- 

 ing and just after their fatiguing work, but such is not the case. 



In 1866, Frankland, 1 studying the sources of muscular power, 

 made numerous calorimetrical determinations of the energy 

 evolved by the combustion of muscle, urea and various foods, or 

 constituents of food, and concluded that the transformation of 

 muscular tissue alone cannot account for more than a small frac- 

 tion of the muscular power developed by animals. 



94. The excretion of carbonic acid. Let us now study the 

 quantities of carbonic acid given off by animals under different 

 conditions of labor and rest. 



The great increase in the carbonic acid exhaled during work, 

 and its decrease with the cessation of work, are clearly brought 

 out in trials by Smith, 2 as shown in the following table: 



Amount of carbonic acid exhaled by the horse under varying condi- 

 tions Smith. 



1 Phil. Mag. 1866, 4th Ser., Vol. XXXII, p. 182; loc. cit. 



2 Jour. Physiology, 1890, No. 1; loc. cit. 



