276 PRINCIPLES OF ANIMAL NUTRITION. 
Rubner makes a slight correction in the above figures for the 
energy of hydration and solution. The energy of the proteids was 
determined in the dry state. They were fed, however, moist, and 
it is known that an evolution of heat takes place when dry proteids 
are brought in contact with water. Consequently the potential 
energy of the moist proteids is less than that computed from the 
calorimetric results. Rubner estimates this loss (loc. cit., p. 307) at 
0.5 per cent. The urea leaves the body in solution. Its solution 
in water, however, causes an absorption of heat equal to 2.4 per 
cent. of the total energy of the urea, and accordingly (neglecting 
other organic matter) the heat value of the urine is higher than that 
calculated from the calorimetric results upon the dried urine. Both 
these errors tend to make the metabolizable energy appear too 
great. Rubner’s corrections are as follows: 
Extrac i 
eer Mext. Lean Meo, Piet 
‘ Cals. Cals. 
Metabolizable energy as above .......... 4.0473 4.4741 3.8889 
Energy of hydration .................. 0.0269 0.0288 0.0269 
MS” © SOUMOD zcuscat acc aavee Gao 0.0199 0.0215 0.0199 
Corrected metabolizable energy ........| 4.0005 4.4238 3.8421 
The energy lost in hydration is, of course, practically a diminu- 
tion of the gross energy of the food. The energy absorbed in the 
solution of the urea can be regarded either as a part of the energy of 
the excreta or as being a part of the general expenditure of energy 
by the body in internal work. (See the next chapter.) 
Rubner * has also computed the metabolizable energy of a num- 
ber of proteids for which direct determinations are wanting. For 
this purpose he uses the results of Stohmann f for the gross energy 
and assumes. first, that the nitrogen will be divided between feces 
and urine in the same ratio as in the experiment on extracted lean 
meat, and second, that the energy of these excretory products per 
gram of nitrogen will be the same as in that experiment. He thus 
obtains the following results: 
* Loc. cit., p. 351. 
} Landw. Jahrb., 13, 513. 
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