There is one more important substance in respect of which great superiority is claimed for brown breads, namely phosphoric acid. From the table on page 122 there can be no doubt that flours containing more of the outer parts of the grain are very much richer in phosphoric acid than white flours, and the disparity is so great that after allowing for the larger proportion of water in brown breads they must contain far more of this substance than do white breads. In the Cambridge digestibility experiments quoted above the proportion of the phosphoric acid digested from the different breads was determined. It was found that for every 100 parts of phosphoric acid in white bread only 52 parts were digested, and that in the case of the brown breads this proportion fell to 41 parts out of 100. Again, as in the case of protein and energy, the phosphoric acid in white bread is more readily available to the body than that of brown bread, but in this case the difference in digestibility is not nearly enough to counterbalance the much larger proportion of phosphoric acid in the brown bread. There is no doubt that the body gets more phosphoric acid from brown bread than from the same quantity of white bread. But before coming to any practical conclusion it is necessary to know two things, how much phosphoric acid does a healthy man require per day, and does his ordinary diet supply enough? From the Board of Trade statistics already quoted it appears that, on the assumption that the average worker eats white bread only, his average diet contains 2·4 grams of phosphoric acid per day, which would be raised to 3·2 grams if the white bread were replaced by bread made from 80 per cent. flour containing ·35 per cent. of phosphoric acid. Information as to the amount of phosphoric acid required per day by a healthy man is somewhat scanty, and indicates that the amount is very variable, but averages about 2½ grams per day. If this is so, the ordinary diet with white bread provides on the average enough phosphoric acid. Exceptional individuals may, however, be benefited by the substitution of brown bread for white, but it would probably be better even in such cases, for the reasons stated when discussing the protein question, to raise the phosphorus content of their diet by the addition of some substance rich in phosphorus but not made from wheat.