Although comparatively little progress has been made by the curative use of rays, other discoveries, of which we have even now passed the brink, will have an enormous effect on medicine and surgery. Already certain kinds of light cure rodent ulcer, one of the most hideous and terrible diseases, not by the importation of fresh substances into the body but by the modification of the tissues themselves. When radiation has been fully studied it will almost certainly be found that the sun, which is the source of practically all terrestrial activity, has been showering upon us, ever since the homogeneous vapour which was the birth-stuff of the universe aggregated itself into worlds and suns and planets, rays which are capable of correcting every sort of disease-germination and, properly used, of preventing it. The absolute deadliness of unmodified sunlight to many sorts of disease-germs is recognised already. The value of sun-baths--the exposure of the whole body, undraped or only lightly covered, to the sunlight--is already discussed in connection with anæmia, chlorosis and the early stages of consumption. When we know just where all disease originates, and why it develops, it seems likely that sunlight and oxygen its child will prevent nearly all disease and cure whatever disease accidentally arises. In place of temporary and dangerous expedients like antiseptics, serum and corrective poisons, we shall import nothing into the human organism, but only exclude what ought to be kept out, and modify into innocuousness what has found its way in. A great part of the disease we call constitutional, as distinguished from infective, arises from food, either because the food itself is not free from disease, or because, from excess in quantity or error in choice, the food we take sets up the production of poisons in the course of digestion, and by yielding, for instance, lactic or uric acid to the blood causes rheumatism or gout, or by introducing into the stomach matter in a state of incipient decay, favours typhoid and other fevers. When, for reasons already indicated, animal food has been eliminated from the menu one great source of disease will have been got rid of.