The difficulties attendant upon the accurate microscopical investigation of enamel and dentine, especially of the latter tissue, have been so great, that very varied views is to their structure and development have been held up to the present time. In the study of the development of dentine, where it is necessary to retain a very oft and delicate tissue, the pulp, in its natural relations to a hard, calcified tissue, he dentine, the difficulties have been greatest, and it has generally been found necessary to resort to decalcification of the hard tissue by acids, to ensure this etention of the natural relations of the parts.