198 PRINCIPLES OF ANIMAL NUTRITION. 
work performed in a manner which can scarcely be explained other- 
wise than as a result of the changes in the latter. The ration con- 
sumed was amply sufficient for the light work of the first and fifth 
periods. When, however, more work was demanded from the 
animal, the live weight promptly fell off, showing that the total 
ration was insufficient. This insufficiency of the total ration Kellner 
believes to be the cause of the increase in the proteid metabolism. 
A consideration of the daily results confirms this view. In 
passing from periods of lighter to those of heavier work the increase 
followed promptly upon the change. In Period III, with the most 
severe work, the proteid metabolism continued to increase through- 
out the period and apparently had not reached its limit at the 
close. Conversely, when the work was diminished in Periods IV 
and V it decreased as promptly as it had increased. Finally, it 
should be noted that the additional amount of proteids metab- 
olized was entirely insufficient to furnish an amount of energy 
equivalent to the increase in the work. 
In four succeeding series of experiments Kellner * has investi- 
gated this phenomenon more fully, some of the sources of error noted 
above having been avoided in the later researches. The results, as 
will appear, still show a deficit of nitrogen. Kellner estimates that 
about 6 grams of nitrogen per day were required for the growth of 
hoofs, hair, epidermis, etc., and believes that there was some loss of 
urinary nitrogen mechanically and chemically. 
Series IT.—In this series of experiments the ration, consisting. 
of 7.5 kilograms of hay and 4 kilograms of beans. was purposely 
made rich in protein. In spite of this liberal supply of protein, 
however, the same result as in the first experiment was noted to an 
even more marked extent. As in the first series, too, the increase 
in the excretion of nitrogen promptly disappeared when the amount 
of work was diminished. 
Series IJJ.—In this series the animal was brought as nearly as 
possible into equilibrium with his food upon rather light work. The 
work was then trebled, while at the same time an addition was 
made to the non-nitrogenous ingredients of the ration by substitut- 
ing for a portion of the beans an amount of oats containing the same 
absolute quantity of protein. In this second period there was a 
slight increase in the digestibility of the protein and, therefore, a 
* Landw. Jahrb., 9, 651. 
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