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IOWA ACADEMY OP SCIENCE 
material to the extract of alcohol-ether which is not fed. At 
any rate, our point is made — ^namely, that there is a marked 
dissimilarity in fats (or what they specifically carry) as regards 
their nutritive value. 
It appears reasonable that inasmuch as there is such a marked 
and peculiar ditference in the nutritive effects of different fats 
difficulty would be experienced in attempting to ideally balance 
an animal’s ration in these respects. Now, it is not altogether 
certain, but it seems entirely reasonable if we base judgment on 
our general physiological knowledge of nutritional problems, 
that not only should there be a difference in the actual amounts 
of total general fat given but that the quantities of the specific 
effective unknown or unknowns necessary may vary considerably 
as animals of different species go through the cycle from egg to 
egg. 
When one must take into consideration the quantity as well 
as the quality of the food constituent in question and likewise 
balance this resultant with various altering demands of the ani- 
mals used, and the general environment during the investigation 
it is readily perceived that the difficulties involved are stupen- 
dous. The ‘‘fat” unknowns are of sufficient magnitude to rather 
discourage those with even iron hearts. 
To attack this problem from the standpoint of appetite, in 
other words, from the standpoint of giving the pigs or otuer 
animals worked with, an opportunity to express their choice, 
would certainly be a logical method of attack. Let it be granted 
that the appetite may sometimes “go wrong”, yet is it not ex- 
cellent policy to give the appetite an opportunity to show wherein 
it is right or wherein it is wrong? 
The great role played by the ash, as determined in the regular 
chemical routine of feeding-stuff analyses, is almost untouched. 
The effects of the phosphorus compounds alone, so well reviewed 
by Forbes^"^, are certainly extensive. 
Then there is the calcium, which comprises more of the min- 
erals of the ordinary body than any other, and about which we 
know comparatively little. Evvard, T)ox, and Guernsey-^ have 
-‘‘Forbes, E. B., and Keith, M. Hr Ion ; A Beview of the Bilcrature of Phos- 
phorus Compounds in Animal Metabolism, 1915, Tech. Bui. 5, Ohio A.?r. Exp. 
Sta. 
‘^Evvard, John M., Dox, A. W., and Guernsey. S. C. : The Effect of Calcium 
and Pi'otein Fed Ih'oenant fn\'ine on Ibe 8i'/.e, Viyor, Bono, Coat, and Condi- 
tion of the Offspring, Am. Jour. Physiol., 1914, XXXIV, 312. 
