The vast amount of literature that is accumulating on this question of vitamins and their deficiency states has, unfortunately, served to confuse rather than to clarify the clinical aspects of this subject. Very few of the publications available to the profession shed a clear light on the problems involved or offer a satisfactory mode of approach to them. One of the principal reasons for the prevalent confusion is the growing use of pharmaceutical preparations containing more than one vitamin. The effects attributed to these multiple agents cannot be evaluated accurately. The only hope of ascertaining fundamental data and bringing order out of this chaos is to abandon the use of compound vitamin preparations in experimental clinical work and employ only known quantities of single, pure substances. Acting on this principle, we have conducted a series of experiments relative to the nature and therapeutic potentialities of the antineuritic vitamin B1