424 PRINCIPLES OF ANIMAL NUTRITION. 
that practically all their potential energy was available to prevent 
loss of tissue. In such experiments, of course, there is no digestive 
work in the proper sense. What they indicate is that what we 
have called rather loosely the work of assimilation for these sub- 
stances is practically zero. Acetic acid, on the other hand, was 
found by Mallévre to increase the consumption of oxygen by from 
10 to 17 per cent., indicating a considerable waste of energy directly 
or indirectly. The general nature of these experiments is not such, 
however, as to afford data of much direct value in relation to the 
question of the availability of the energy of ordinary foods. 
Timotuy Hay.—The experiments described in the foregoing 
paragraphs relate to pure or nearly pure nutrients. Experiments 
upon a steer have been made by the writer in conjunction with 
Fries in which the availability of the apparent metabolizable energy 
of timothy hay has been determined. To a basal ration consider- 
ably below the maintenance requirement, consisting of 3250 grams 
of hay and 400 grams of linseed meal, three different additions of 
timothy hay were made, the digestibility of the ration in each 
period being determined, and likewise the total balance of nitrogen, 
carbon, and energy by means of the respiration-calorimeter. The 
results as to energy, uncorrected for the very small differences in 
the organic matter of the basal ration consumed and for the 
changes in the live weight of the animal, were as follows: * 
Period A. Period B. Period C. Period D. 
Outgo, |Income,| Outgo, |Income,| Outgo, |Income,| Outgo, |Income, 
Cals. 
Cals. | Cals. s. Cals. Cals. Cals. Cals. 
Feed eis ois ais ee a aie, |e ene 14,923)...... 20,297|...... 25,198). ..... 29,647 
Excreta: 
Feces.......... 6,446)...... 8,590]. ..... 11,477). 0.2... 14,276 
Urine. « os es ses 863]...... OTA ls cede 5 1,125)...... 1,220 
Methane...... 996]...... 1,251)...... 1,374]...... 1,896 
Metabolizable ...| 6,618]...... 9,482)...... 11,222). ..... 12,255 
14,923) 14,923] 20,297| 20,297] 25,198] 25,198] 29,647| 29,647 
Metabolizable ...]...... 6,618)...... 9,482|}...... 11,222]...... 12,255 
Heat produced ..] 9,067]...... 10,206]...... 10,606]...... 11,183 
Gain or loss......]...... 2 AAD) ess 724 616}...... 1,072 
9,067) 9,067) 10,206] 10,206) 11,222) 11,222] 12,255) 12,255 
* Proc. Soc. Prom. Agr. Sci., 1902. 
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