presumably consequent greater or less degree of exposure to the causative agent.
Age.— Hitherto pellagra was considered to be a disease of middle age, the majority of cases occurring between 20 and 50. Sambon has shown that within the endemic centres children are attacked, and that no age is exempt, he having seen the characteristic symptoms in a woman over 100 years old and in infants of barely 3 months.
Occupation.— The disease is most prevalent among field-labourers. The inhabitants of towns, even of those in the very heart of intensely pellagrous districts, enjoy an immunity similar to that of town-inhabitants as regards malaria. Felix points out that pellagra is quite exceptional among the Jews, who, as a race, rarely engage in agriculture. Bouchard says that herdsmen in pellagra regions are exempt. Although pellagra occurs most frequently in rural labourers living from hand to mouth, it does attack people in good circumstances. This has long been recognized in Italy, and the figures given by Gruner for the southern States of the United States— 258 cases had lived in poverty, 59 in comfort, 6 in affluence— show that the same remark applies to America.
Season.— Of all diseases with marked seasonal connection, pellagra is one of the most striking. As in the case of malaria, the pellagra season varies in different localities, but is always the same in the same locality.
In Europe the disease invariably appears in manifest and epidemic form during the spring and autumn quarters of the year, the spring outbreak being by far the most severe, the autumnal recurrence often inconspicuous or lacking. In Egypt, according to Chalmers, there is a spring invasion occurring in the months of April and May, and an autumn recurrence in November. In Nyasaland, according to Dr. Stannus, pellagra seems to prevail chiefly during August, September, and October, which are the spring months in the southern hemisphere, and again, though to a less extent, in January, February, and March (fall recurrence). In the United States of America, owing to the vast extent of territory and great variety of climates, the periodical incidence of the disease is necessarily different in different sections. In the northern States, as in
