The underlying factors concerned in the prevalence of pellagra fall into two classes, which from the standpoint of public health must be viewed from different angles. There is a small, but not an inconsiderable, number of cases which arise from conditions peculiar to the individual. Among these are dietary eccentricities and idiosyncrasies, food fads, obsessions, alcoholism, gastro-intestinal disease and other disturbances resulting in a disordered diet. These are isolated, or sporadic, cases and may occur anywhere, at any season and without reference to financial status or dietary surroundings. Conditions of this nature do not usually come within the scope of public health activities, and such cases may therefore be excluded from further consideration in this connection. Their prophylaxis and treatment are matters for the attention of the family physician. On the other hand are the cases which arise from conditions more or less common to groups of individuals, such as