AGRICULTURE: HART, AND OTHERS 
375 
is very materially increased through a proper adjustment of the normal 
factors of nutrition. 
With this recognition of all the normal factors for adequate nutrition 
there must not simultaneously arise a desire for a mathematical expres- 
sion of these factors in feeding standards. It is doubtful if this can 
ever be done, at least for certain of them. For example, the role of 
the mineral nutrients is so varied, including such widely separate func- 
tions as construction and control through antagonism as to make it 
seem futile to attempt an expression of absolute requirements when 
natural foods, with their diversity of mineral content, are involved. 
Even the recognition of differences in the quahty of proteins and their 
relation to nutrition^ will make it more difficult to continue expressing 
protein requirements in exact quantities than before the development 
of such knowledge; and what can be said of the quantitative require- 
ments of fat soluble A and water soluble B and their supply in feeding 
materials? 
All these developments of the last few years emphasize the need of a 
thorough study of the contributing nutritive factors of a single food 
stuff, and in the state of our present knowledge such information will 
be secured only by physiological tests, involving the animal in reproduc- 
tion and milk secretion. A contributing factor by a natural food may 
at times be in the nature of toxicity and this may serve as a harmful 
and abnormal factor. As such knowledge develops and it becomes 
clear that this or that single food material will supply adequately the 
normal nutritive factors, not measurable by any quantitative chemical 
method, such as fat soluble A, water soluble B, or mineral nutrients, we 
will return with more confidence to the mathematical standard that 
only involves the energy and protein supply of that single food material. 
This confidence in the expressed quantities of energy and protein avail- 
able in a food-stuff will rest upon the definite information that they 
become physiological effective only when they form part of a ration 
which carries one or a number of food-stuffs supplying adequately the 
other nutritive factors. With such an understanding the feeding stand- 
ards developed on the energy-protein basis would continue to be theo- 
retically sound and of very great practical value. As illustrative of 
our position, and taken from our own experience with wheat grain feed- 
ing we would feel reasonably safe if a wheat grain ration, based on pro- 
tein and energy and to be fed continuously to a growing herbivorous 
animal, was built around alfalfa hay; less safe if built around com 
stover, and fearful of disaster should the roughage used be wheat straw. 
In our earlier experiments a 'balanced' ration from the wheat plant 
