BALANCED DIETS
199
any other measurement (such as blood hemoglobin) that may be pertinent to the
problem at hand, and the pair mates are then fed the same amount of the two
rations to be compared, one to one animal and one to the other. Under these
conditions the better balanced of the two rations will promote the more rapid
growth, or in other ways induce a better nutritive condition, for example with
reference to the blood or the bones ; and conversely every improvement in a diet
with respect to its power to promote growth and nutritive condition is prima facie
evidence of a betterment in its balance. The reality of this conclusion seems
obvious, and no precise definition of balance in diet on any other basis has been
proposed in so far as the writer is aware. In fact, a search of current writings and
text-books has failed to reveal that the conception of nutritive balance in diets or
rations has received much intensive thought. On the evidential side, the con-
clusion is supported by the results of numerous paired-feeding experiments, which
have demonstrated the possibility of distinguishing on this basis better from poorer
balanced diets with respect to protein, vitamins, sugars and inorganic salts.
Of the balanced ration, it may be said that the more of it is consumed, the
better nourished will be the animal with reference to which the ration is balanced,
up to the point of repletion of its requirements. It is an attractive hypothesis
concerning unbalanced rations that the more of them are consumed the poorer
nourished will be the animal with reference to the functions with respect to which
the rations are unbalanced. To the writer the hypothesis has much rational appeal
and it receives factual support from some experiments performed in the nutrition
laboratory at the University of Illinois. Thus, young growing rats subsisting on a
diet of milk will develop anemia, because milk is unbalanced with respect to the
requirements of the hematopoietic tissues; and furthermore the more milk the
animals consume daily, the more rapidly will the anemic condition develop,
although in all other respects the animals are well nourished. Again, young rats
placed upon a diet high in calcium, low in phosphorus and deficient in vitamin D
will develop rickets, and the rate of development of this bone disease is the greater,
the greater the daily consumption of the rachitogenic diet. Of much the same
significance is the fact that young pigs placed upon a protein-deficient diet will
grow slowly, but with increasng intakes of food will become increasingly fat, re-
presenting a misdirected or uncoordinated growth. Probably further illustrations
of the hypothesis that unbalanced rations, like toxic substances, exert harmful
effects in proportion to the amounts consumed, will be forthcoming when it is
subjected, to systematic and quantitative study. The quite general failure
of animals to consume unbalanced rations as avidly as balanced rations is under-
standable if the former may be considered physiologically harmful.
Some of the implications of the above conceptions of nutritive balance in diet
are interesting and of importance to the science of nutrition. Attention will be
restricted to the question of the utilization of the chemical energy contained in a
diet, representing a nutritive summation of all the organic nutrients.