Some of the activated olive oil, which had been stored in a stoppered bottle, showed no change in potency ten months later. It was found also that the fats might be activated by the rays from the open carbon arc, the iron arc, and sunlight; but that exposure for such prolonged periods as 17 hours destroyed their potency. This destruction took place even on cod liver oil.[5] It has long been known that human tissue is more actively changed by light when it has been “sensitized.” Quinine, esculin, fluoresceine, etc., are examples of tissue sensitizers, in addition to their other effects. The most powerful of all known sensitizers is haemato-porphyrin—or simply “porphyrin.” This sensitizer is a purple substance closely allied to the haemoglobin that gives blood its red color. Subtracting its iron and albumin from haemoglobin by appropriate chemical processes leaves porphyrin. This substance reacts strongly to the ultra-violet rays, in rare cases causing a disease which turns the teeth to a deep purple hue. Victims of this uncommon ailment have to wear gloves constantly, and when going out of doors during the day time must put on heavy veils.[6] Porphyrin is capable of dissolving the red corpuscles of the most dissimilar animals in the presence of sunlight. But neither the haemato-porphyrin nor the light alone is capable of injuring the animals. Only the combined effect of the two can harm them. A physician experimentally injected an exceedingly minute quantity into himself and then exposed himself to a moderate light, and became very ill. Hausmann found that even the diffused sunlight of an early spring day in Vienna was sufficient to cause the death of white mice which had been subjected to small quantities of this strange substance. Dr. E. C. Van Leersum, of Holland, proved by experiments with rats that the utilization of lime by our bodies can be controlled almost at will by this “sensitization” process. Rickets, or a condition indistinguishable from rickets, can be produced or cured by proper control of the sensitization. SUNLIGHT AND INFANTILE PARALYSIS An article by Science Service, quoted in _Science_, September 11, 1925, says: Another of the dreaded diseases of childhood, infantile paralysis, which, like rickets, graduates large quotas of cripples, has responded to the good influence of the sun’s rays. Dr. G. Murray Levick, medical director of the Heritage Craft Schools at Chailey, Sussex (England), who originated the treatment, said that no other method has ever had as good results as this in the treatment of infantile paralysis.