The investigation, of which the results are recorded in the following pages, was carried out in the Physiological Laboratory of the Owens College, at the suggestion and under the direction of Professor Arthur Gamgee. The elaborate investigations of Roscoe had placed vanadium amongst the metals whose chemical characters and relations have been rigidly investigated; they had shown that vanadium is to be ranked as a member of one of the most interesting families of elements, and yet not a single fact had been ascertained in reference to its physiological action. The hope that an elaborate examination of the physiological reactions of vanadium might cast some light upon the relations which may exist between the chemical and the physiological affinities of elements, and the fact that Professor Roscoe offered to furnish any vanadium compound which might be required, acted as inducements to undertake this research.