It does not follow, however, from the fact that gliadin, hordein, or zein is inadequate as a sole protein food, that wheat, barley, maize, or their mill products would be correspondingly inadequate even if fed alone. Each of these grains (and of the staple mill products made from them) contains a mixture of proteins, and the other proteins with which gliadin, hordein, and zein are always mixed in wheat, barley, and maize do not show these same peculiarities of chemical structure, so that we have no reason to fear that either lysine or tryptophane would ever be wholly lacking in any staple food product made from grain. Thus glutenin, which is always present in wheat flour, has been shown to be adequate for both maintenance and growth even when it was the only protein in the diet. It is, however, only reasonable to expect that the mixture of proteins found in corn meal or even wheat flour will be of somewhat less value in nutrition than an equal weight of the mixture of proteins which we find in milk, eggs, or meat.

Fortunately the proteins of milk are relatively rich in those amino-acid radicles in which the grains are poor. Osborne and Mendel have found that their animals are not only maintained in health and vigor, but also make a normal rate of growth when three fourths of their protein is zein and one fourth is lactalbumin. If bread be made with milk instead of water, or if breakfast cereal or even corn meal mush be eaten with cream or milk, the protein of the combination may have fully as high a value in nutrition as the average protein of ordinary mixed diet.

In connection with wheat-saving by substitution of other cereals during the war, the question of the equivalence of the different food-grains and particularly of corn with wheat in nutrition became a matter of some importance.

The investigations of McCollum, in which laboratory animals have been kept on restricted diets often for a lifetime, and in several cases for more than one generation, seem well calculated

to bring to light any differences in the more obscure factors of food value or in general wholesomeness of the two grains, if any such differences exist. In summaries of the results of an extended series of such experiments, McCollum repeatedly has stated that wheat and maize are very similar in their dietary properties. If this seems surprising in view of the well-known inadequacy of zein when fed as the sole protein of the diet, it should be recalled that Osborne and Mendel, to whom our knowledge of the nature of this deficiency of zein is so largely due, have demonstrated also that the other important protein of corn, maize glutelin, is adequate to meet all protein requirements and maintain a normal rate of growth when fed as the sole protein of the diet. They have also shown that zein, while inadequate alone, may yet take the major part in meeting protein requirements either of maintenance or of growth, when it is supplemented by a much smaller amount of milk protein.

As the result of their further studies with rats, Osborne and Mendel have also found the proteins of barley, oats, rye, and wheat to be about equally efficient in promoting and supporting growth.

Wheat, maize, and oat proteins all showed essentially the same efficiency in human nutrition experiments carried on in the writer's laboratory.

The evidence at present available makes it appear probable that there is this slight difference, that in wheat and oats the first limiting amino acid is probably lysine, while in maize tryptophane is probably the first and lysine the second limiting amino acid.

Experiments by Osborne and Mendel have shown that the proteins of entire wheat have a much higher nutritive efficiency than an equal weight of the proteins of patent flour.

Kramer and St. John have found that the heating involved in toasting bread does not lower the nutritive efficiency of its protein.

The digestibility of the grain proteins when fed free is probably not inferior to that of animal protein. It is evidently very largely because of the associated substances, such as cell walls which still inclose the grain proteins to a certain extent in ordinary mill products, that the coefficient of digestibility of the protein of bread, for example, is lower than that of an average mixed diet. Partly for the same and partly for other reasons, it was anticipated that the coefficient of digestibility of whole grain products might be somewhat lower than that of the finer products representing only the inner portion of the kernel.

This question was of particular interest as affecting the comparative food values of patent, "entire wheat," and Graham flours and the breads made from them. The average results of a long series of digestion experiments carried out under the auspices of the United States Department of Agriculture were as shown in Table 46.

The lower coefficients of digestibility of the "entire wheat " and Graham flours almost exactly offset their higher protein contents, so that it may be said that the amount of protein digested and absorbed from a pound of one of these or from a pound of patent flour is practically the same. The amount of available energy is also about the same in either case. However, as Woods and Merrill have pointed out, it does not follow that a

larger amount of digestible nutrients may not be obtained from a given amount of wheat when milled as Graham flour or as entire wheat flour than when ground for patent flour, because 100 pounds of cleaned and screened wheat will yield 100 pounds of Graham flour, or about 85 pounds of " entire wheat" flour, but only about 70 pounds of patent flour. It follows that if milled on an equally large scale, i.e. if there were an equally large demand, Graham and " entire wheat " flours could be sold at a lower price than patent flour, but at present they usually cost as much, or in some cases even more.

Regarding the coarser and finer flours simply as sources of protein and energy, they are so nearly equal both in digestible nutrients and (at present, to the individual consumer) in pecuniary economy1 that they may be regarded as substantially equivalent and interchangeable. They are, however, quite different as sources of mineral elements and vitamin B and somewhat different in their effect upon the digestive tract.

The coarser wheat products stimulate peristalsis more than do the fine flour products, an effect which is desirable in some persons and undesirable in others. This property of the whole wheat products is often attributed to mechanical irritation, but cannot be due entirely to this, because "bran mash" is used as a laxative with horses whose other food (hay, for example) would certainly furnish more mechanical stimulation than the bran. The wheat kernel contains two distinct substances reported as having laxative effects which are largely rejected in the preparation of fine flour. These are the oil of the germ and the phytin (one of the phosphorus compounds) which is especially abundant in the bran. It is probable that in man the stimulation of peristalsis by whole wheat products is due in part to direct mild laxative action by one or both of these constituents, and in part also to the mechanical effect of the fibrous particles.

This, of course, does not apply to certain proprietary "whole wheat" products sold at high prices.

The ash constituents of the grains are largely concentrated in the germs and outer layers. This has been pointed out with respect to barley, maize, and rice earlier in the chapter. We shall therefore consider wheat chiefly at this point. Bran yields 10 to 20 times as much ash as patent flour. Comparing the patent flour with the whole wheat, the discrepancy is still large, the wheat containing 3 to 5 times as much of iron, of phosphorus, of calcium, or of total ash as the fine flour made from it. Thus three fourths of the ash constituents of the wheat kernel are lost to man in the process of manufacturing the wheat into white flour. Doubtless the loss in digestion is somewhat greater for the coarser than for the finer products in the case of the ash constituents as of the proteins, but there is no reason to suppose that the loss in digestion would in any case approach the loss involved in the ordinary milling process. The body probably absorbs from a pound of genuine whole wheat bread at least twice as much phosphorus, iron, and calcium compounds as from a pound of white bread. No adequate experiments upon this point appear to have been made with man, but Bunge 2 has tested the value of the ash constituents of the bran for growing rats.

Eight young rats of the same litter and approximately the same size at the beginning of the experiment were divided into two groups of four each. One group was fed on white bread which contained 0.0015 per cent iron, 0.032 per cent calcium, and 0.12 per cent phosphorus; the other group on whole wheat bread which contained 0.0055 per cent iron, 0.055 per cent calcium, and 0.39 per cent phosphorus. The rats receiving the whole wheat bread grew much better than those fed on white bread, and were found to contain at the end of the experiment both a larger amount and a higher percentage of hemoglobin. It was clear that the ash constituents of the outer layers of the

1 The ordinary digestion experiments taken alone are useless if not positively misleading for this purpose because of the excretion in the feces of ash constituents which have been absorbed and utilized in the body.

2 Zeitschrift für physiologische Chemie, Vol. 25, page 36 (1898).