332 PRINCIPLES OF ANIMAL NUTRITION. 
implied in this that the metabolizable energy of the digested nitro- 
gen-free extract is the same as its gross energy. 
Summary.—The results recorded in the preceding paragraphs 
regarding the metabolizable energy of the several classes of digesti- 
ble nutrients are summarized in the following table: 
METABOLIZABLE ENERGY OF DIGESTIBLE NUTRIENTS. 
Cattle, Horse, Swine, 
Cals. per Cals. per Cals. per 
Grm. Grm. Grm. 
Protein (N X 6.25): 
From wheat gluten ................000- 4.894 
ie es BEN ROSA) aes Stee nine oe 4.958 
“beet molasses..............000005 3.984 
SAMOA BRAIN seas scons cs sa: Sead eaasaileiallaead ¥avend. 2 allem ae, 8 ea hae 4.083 
ie “ration of oats, hay, and straw 3.228 
"meadow hay ..............2.005- 1.272 
“timothy hay ................005. 3.057(?) 
© SCTAW' 5, axed bee aee BEER wh ee nls eS (?) 
Fat: 
From peanut oil...................0005 8.821 
“hay (ether extract)............... 3-322 
Carbohydrates : 
Starch, Kellner’s experiments ........... 3.763 
«  Kihn’s bre cota a eeaee 3.648 
Nitrogen-free extract (assumed) .........)......... 4.185 
Crude fiber, of extracted straw .......... 3.606 
* “hay fed alone............. 3.311 
i «added to basal ration .| 3.606 
ef OS SES OB SUP AW: 2h utiel a Acaea ince ioe ae 3.437 
ng «wheat straw ............. 3.001 
sf se 88 MEK EC TAtION: to 36 apa'evis ws dis We Sede oo 3.523 
Perhaps the most striking thing about these figures is the wide 
range of the results upon the same class of nutrients. For reasons 
already stated, this is most noticeable with the protein, but it is 
sufficiently marked also with the other two groups. Moreover, 
such meager data as we possess regarding other animals than the ox 
indicate that the results vary with the species of animal, a fact 
which should not surprise us, but which, nevertheless, adds mate- 
rially to the complexity of the subject and greatly widens the range 
of necessary investigation. It is obvious, therefore, that at present 
our knowledge is too imperfect to allow of the assignment of average 
values for the metabolizable energy of the different classes of 
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