We have already reported data obtained from studies on the effects on dentition of alterations of calcium and phosphorus metabolism.(1, 2, 3). Here it was shown that disturbed inorganic salt metabolism is a very important factor through which the pulp and the integrity of the calcified tissues of the teeth may be affected. From the results obtained in our animal experiments, we have expressed our conviction that dental caries as a disease, manifesting itself clinically as a lesion of the enamel of the tooth, is usually associated with a distinct disturbance of the pulp (1, 2, 3). The latter was described as (a) pulpal engorgement; (b) serous degeneration of the odontoblasts; (c) fibrosis; (d) necrosis. In teeth displaying these pulpal pathologic changes, radiolucent zones were observed in the dentin and enamel, which in the radiograph, assume the characteristics of dental decay although, these teeth at first, present no gross surface lesions. It is only after a long continued pathology that lesions in the enamel can be seen clinically (3). We have found that by disturbing the calcium-phosphorus ratio in the blood, regardless of the mechanism, we could induce the described pulpal pathology, which on prolongation of the experiment is followed by enamel caries.Since the calcium-phosphorus metabolism is greatly influenced by the endocrine glands, a study of the internal secretions seemed advisable. There has been much speculation as to the relationship of the endocrines to the erupted dentition. In 1911, Erdheim (4, 5) studied the effects of parathyroidectomy on the incisors of rats. He observed that the teeth became opaque and brittle; the enamel and dentin were hypoplastic; blood vessels were present in the predentin and bands