=Pellagra.=--The precise ætiology of pellagra being still unknown, treatment of the disease can only be empirical. From this point of view blood transfusion has been tried by Cole, who began using it in 1908. The results in twenty cases have been reported, and are distinctly encouraging. All the transfused patients were in the last stages of the disease, but nevertheless a recovery rate of 60 per cent. was obtained, the usual rate being 10 to 20 per cent. In the present state of knowledge comment is scarcely possible, but if pellagra is, as some observers have suggested, a “deficiency disease,” it may be supposed that the transfused blood provides a temporary supply of the substance that is lacking; the patient is thus enabled to start along the road to recovery. CHAPTER IV DANGERS OF BLOOD TRANSFUSION Appreciation of the dangers attending the practice of blood transfusion has varied greatly at different times. In the seventeenth century a happy ignorance took no account of them whatever. In the eighteenth century they were so greatly feared that transfusion fell into abeyance. In the nineteenth century it was realized that dangers existed, but they were imperfectly understood; when fatalities occurred, a partial knowledge explained them away more easily than our fuller knowledge can to-day, so that transfusion was practised in spite of them. At the beginning of the twentieth century, with the discovery of “blood groups,” it was thought that all danger had been eliminated. At the present time the pendulum is swinging back again, and the problem of the complete elimination of danger is proving more complex than it was thought to be a few years ago.