Make a portion of oatmeal-porridge in the usual manner, but unusually thick—a pudding rather than a porridge; then, while it is still hot (150° or thereabouts) in the saucepan, add some _dry_ malt flour (equal to one-eighth to one-fourth of the oatmeal used). Stir this dry flour into it and a curious transformation will take place. The dry flour instead of thickening the mixture acts like the addition of water, and converts the thick pudding into a thin porridge. I find that this paradox greatly astonishes the practical cook. FOOTNOTE: [22] I have lately learned that a patent was secured some years ago for ‘malt bread,’ and that such bread is obtainable from bakers who make it under a license from the patentee. The ‘revised formula’ for 1884, which I have just obtained, says: ‘Take of wheat meal 6 lbs., wheat flour 6 lbs., malt flour 6 oz., German yeast 2 oz., salt 2 oz., water sufficient. Make into dough (without first melting the malt), prove well, and bake in tins.’ CHAPTER XIX. THE PHYSIOLOGY OF NUTRITION. I HAVE repeatedly spoken of the nitrogenous and non-nitrogenous constituents of food, assuming that the nitrogenous are the more nutritious, are the plastic or flesh-building materials, and that the non-nitrogenous materials cannot build up flesh or bone or nervous matter, can only supply the material of fat, and by their combustion maintain the animal heat. In doing so I have been treading on loose ground—I may say on a scientific quicksand. When I first taught practical physiology to children in Edinburgh, many years ago, this part of the subject was much easier to teach than now. The simple and elegant theory of Liebig was then generally accepted, and appeared quite sound. According to this, every muscular effort is performed at the expense of muscular tissue; every mental effort, at the expense of cerebral tissue; and so on with all the forces of life. This consumption or degradation of tissue demands continual supplies of food for its renewal, and as all the working organs of the animal are composed of nitrogenous tissue, it is clearly necessary, according to this, that we should be supplied with nitrogenous food to renew them, seeing that the nitrogen of the air cannot be assimilated by animals at all. But besides doing mechanical and mental work, the animal body is continually giving out heat, and its temperature must be maintained. Food is also demanded for this, and the non-nitrogenous food is the most readily combustible, especially the hydro-carbons or fats; the carbo-hydrates—starch, sugar, &c.—also, but in lower degree. These, then, were described as fuel food, or heat-producers.