The Island of Lewis in the Hebrides is of very great interest in illustrating the greater importance of nutrition than of hygienic factors, in promoting health, in reducing the infant mortality and in preventing skeletal defects. It has already been pointed out that the natives of this island subsist on a diet consisting in great measure of cod's heads stuffed with cod livers, milk, fish, turnips, oat meal and potatoes, and that their diet is in great measure a carnivorous one, supplemented with small additions of cereal, tuber and root vegetables. They live under the worst conceivable hygienic conditions, with a filthy byre in one end of the dwelling, with no window or only a fixed one and with a peat fire constantly burning, the smoke of which can escape only through the thatched roof and through the open door. The babies are taken out of doors only for a few minutes at a time in bright weather, are deprived of sunlight and breathe an atmosphere sufficiently smoky to make inflamed eyes the rule, yet they remain practically free from rickets. The death rate of infants in the island has not infrequently fallen as low as any place in the British Isles. The influence which counteracts the bad hygienic conditions is the universal practice of breast-feeding, and by mothers whose diet, although unattractive to the palate of the average European or American, is, when evaluated on the basis of its biological value as shown by experiment, a highly satisfactory one. Such illustrations as the foregoing are very convincing evidence that the diet is the factor of primary importance in the etiology of rickets, and this belief is fully established by the experimental production of rickets and related skeletal defects in animals, when the diet was the sole cause to which the abnormalities of the bones could be attributed.

Several observers have recently reported the successful treatment of rickets by radiation with the rays from a mercury vapor lamp (very short rays), and with sunlight (29). It is necessary, therefore, that any discussion of the etiology of rickets, to be convincing, must satisfactorily account for the tendency for rickets to heal under such treatment. We have now an observation of extraordinary interest which is suggestive of the nature of the "cure" which is effected by light treatment. Further studies will be necessary before a conclusive statement can be made relative to this matter, but the observation in question helps to clarify our views on this seemingly conflicting evidence concerning the importance of light as a means of preventing rickets.