It has been shown for instance by Dr Hopkins in Cambridge, and his results have been confirmed at the Carnegie Institute in America, that young rats fail to thrive on a diet composed of suitable amounts of purified protein, fat, starch, and ash, but that they thrive and grow normally on such a diet if there is added a trace of milk or other fresh animal or vegetable substance far too small to influence either the protein content or the energy-value. Another case in point is the discovery that the disease known as beri beri, which is caused by a diet consisting almost exclusively of rice from which the husk has been removed, can be cured almost at once by the administration of very small doses of a constituent existing in minute quantities in rice husk. The suggestion is that high grade flours, like polished rice, may fail to provide some substance which is necessary for healthy growth, a substance which is removed in the germ or husk when such flours are purified, and which is present in flours which have not been submitted to excessive purification. The answer is that no class in Great Britain lives on bread exclusively. Bread appears from the government statistics already quoted to form only about half the diet of the workers of the country. Their diet includes also some milk, meat, and vegetables, and such substances, according to Dr Hopkins’ experiments, certainly contain the substance, whatever it may be, that is missing from the artificial diet on which his young rats failed to thrive. One last point. It will have been noticed in the figures given above that the variations in protein content, digestibility, and energy-value, between different kinds of bread are usually not very large. There is, however, one constituent of all breads whose proportions vary far more widely, namely water. During last summer the author purchased many samples of bread in and around Cambridge, and determined the percentage of water in each sample. The samples were all one day old so that they are comparable with one another. The results on the whole are a little low, probably because the work was done during a spell of rather dry weather, when the loaves would lose water rapidly. The average figures are summarised below: Percentage of water Cottage loaves made of white flour 31·7 Tinned loaves made of white flour 32·7 Small fancy loaves made of white flour 33·7 Tinned loaves made of “Standard” flour 35·9 Tinned loaves made of brown or germ flour 40·0