As the papers of this series are planned to be a continuation of those of an earlier series, no attempt will be made here to review at all completely the voluminous literature bearing on the physiology of vitamin B1. The historical development of the subject, the various methods which may be followed in assaying for this vitamin, the importance of the vitamin for growth, lactation and other functions, and similar topics concerning which our fundamental knowledge has been established for many years—all of these will be omitted from the present discussion. Instead, the objective will be to survey briefly the more recent contributions to knowledge in this field, to summarize as briefly as possible the present points of view concerning the relation of vitamin B1to various bodily functions, to describe the unique function of this dietary factor, if there is such, and, finally, to indicate wherever possible the