At present it is the almost universal belief that infantile tetany is a manifestation of rickets. Whereas in rickets the usual blood picture is that of a low inorganic phosphorus and normal calcium content, in tetany the reverse is true, the blood phosphorus being normal or increased and the blood calcium low.1 The deficiency of the calcium ion has been proved to be the direct cause of the symptoms of tetany.2 Huldschinsky3 first showed, and others after him, that tetany was often a sequel of rickets inadequately treated. In a recent article Gerstenberger and his co-workers4 demonstrated by means of roentgenologic studies and chemical analyses of the blood that interrupted or imperfect antirachitic treatment induced tetanic symptoms in the rachitic child. In their studies the presence of rickets was first proved by roentgenograms of the bones and by a low inorganic blood phosphorus. Insufficient ultraviolet therapy