106 PRINCIPLES OF ANIMAL NUTRITION. 
approximately, according to Rubner (see Chapter X), 321 Cals. of 
available energy. The actual expenditure of energy by the animal 
was not determined, but is estimated by the author on the basis 
of Rubner’s investigations at about 1280 Cals. 
Several experiments by Rubner * lead to the same conclusion. 
In these experiments the carbon and nitrogen of the excreta were 
determined and the nitrogen of the food estimated from average 
figures. The proteid metabolism having been computed from the 
total excretory nitrogen, the corresponding amount of carbon is 
computed from the average composition of the proteids and any ex- 
cess in the excreta is assumed to be derived from the metabolism 
of fat. (Compare p. 78.) The following are the results in brief, 
including the one cited above (p. 104): 
; Nitrogen| Fat 
rn ea Romar. 
Grms.’ | 2xereta, olized, 
Grms. | Grms. 
Nothing .............| ..-- 4.38 | 49.33 
415 grms. lean meat ...| 14.11 | 13.72 | 25.44 | Average of several days, 
Nothing: &. csaeteniaoad Sewies 2.80 | 79.94 
740 grms. lean meat ...| 25.16 | 20.63 | 30.73 | Ist two days of feeding. 
Nothing s.icsseedeca sl eee uc 5.25 | 84.36 
740 grms. extracted lean ; 
MEAG cies sisane orate 35.22 | 26.37 | 28.37 | 1st to 4th day of feeding. 
Nothitige 24 ssesagacdall a0a3 1.08 | 22.88 
390 grms. lean meat ...| 13.26 | 8.53 | 11.42 | 1st day of feeding. 
Nothing $2: cccnsvcdes| aices 1.08 | 22.88 
350 grms. lean meat ...; 11.90 | 10.10 , 11.79 | 3d to 6th day of feeding. 
Nothing: 00 es se0ee.00) 23085 3.50 | 37.24 
580 grms. lean meat ..| 19.72 | 18.47 | 21.45 | 1st to 7th day of feeding. 
While some of the experiments were hardly continued long 
enough to absolutely establish the sufficiency of the proteid supply, 
nevertheless we see in all cases a material loss of fat on rations which 
apparently are sufficient to prevent a loss of nitrogen from the 
body. 
Tt should perhaps be noted that in Pettenkofer & Voit’s ex- 
periments 1000 grams of meat nearly prevented a loss of nitrogen 
* Zeit. f. Biol., 22, 43-48; 80, 122-134. 
