The year 1920, then, has brought us to a recognition of at least three members of the family. Still more recently another deficiency disease has been under investigation and Hess has found in cod-liver oil a remedy for rickets that he cannot believe owes its efficiency to the "A" type. Mellanby of England believes the "A" vitamine is the preventive factor in this disease but Hess's results at least suggest the possibility that the antirachitic vitamine may be separate and distinct from any of those yet named, possibly vitamine "D?" Others are beginning to doubt the identity of the rat growth promoter and the beri-beri curing complexes and feel that the "B" itself may be the name of a group instead of a single entity. All of these features make one feel uncertain to say the least, as to the limits of this vitamine family or of the future possibilities but enough has been given to indicate the historical development to date and we can now turn to more special features of the subject and their bearing on every day affairs. CHAPTER II THE ATTEMPTS TO DETERMINE THE CHEMICAL NATURE OF A VITAMINE The discovery of the existence of an unknown substance is naturally a stimulation to investigation of its nature. In the case of the vitamines we have many researches to this end but extremely meagre results. We are today actually no nearer the goal of identification than we were in 1911 when Funk published his studies on the beri-beri curing type. In brief, we do not know what a vitamine is. Nevertheless, it will be of interest to the student to review the attempts that have been made to isolate these substances for such attempts must furnish the starting point for further studies and their description will help to make clear the nature of the problem involved.