In actual practice, however, it generally happens that the higher grade flours are made from a blend of wheats containing a considerable proportion of hard foreign wheats which are rich in nitrogen, whilst wholemeal and standard flours are usually made from home grown wheats which are relatively poor in nitrogen. From a number of analyses of foreign and home grown wheats it appears that the relative proportions of protein is about 12½ per cent. in the hard foreign wheats as compared with 10 per cent. in home grown wheats. Thus the presence of a larger proportion of protein in the hard wheats used in the blend of wheat for making the higher grade flours must tend to reduce the difference in protein content between say patents and wholemeal flours as met with in ordinary practice. Furthermore much of the bread consumed by that part of the population to whom a few grams per day of protein is of real importance is, or should be, made, for reasons of economy, from households flour, and the disparity between this grade of flour and wholemeal flour is much less than is the case with patents. It appears, therefore, on examining the facts, that there is no appreciable difference in the protein content of the ordinary white flours consumed by the poorer classes of the people and wholemeal flour or standard flour. In the above paragraphs account has been taken only of the total amount of protein in the various kinds of bread and flour. It is obvious, however, that the total amount present is not the real index of food-value. Only that portion of any article of diet which is digested in the alimentary canal can be absorbed into the blood and carried thereby to the tissues where it is required to make good wear and tear. The real food-value must therefore depend not on the total amount of foodstuff present but on the amount which is digestible. The proportion of protein which can be digested in the different kinds of bread has been the subject of careful experiments in America, and lately in Cambridge. The method of experimenting is arduous and unpleasant. Several people must exist for a number of days on a diet consisting chiefly of the kind of bread under investigation, supplemented only by small quantities of food which are wholly digestible, such as milk, sugar and butter. During the experimental period the diet is weighed and its protein content estimated by analysis. The excreta are also collected and their protein content estimated by analysis, so that the amount of protein which escapes digestion can be ascertained. The experiment is then repeated with the same individuals and the same conditions in every way except that another kind of bread is substituted for the one used before. From the total amount of protein consumed in each kind of bread the total amount of protein voided in the excreta is subtracted, and the difference gives the amount which has been digested and presumably utilised in the body. From