On the histological evidences of the organic content and reactions of marsupial enamel, with a note on human enamel

During histological investigation of the organic content of human enamel it was noticed that portions of young human enamel (Plate 33, fig. 1) which had been permeated by stain from the dentine aspect were permeable through about three-fourths of their thickness and so looked structurally very similar to marsupial enamel treated in the same manner (fig. 2), the chief differences being the direction of the prisms, and the degree and regularity of patency of the inter-prismatic substance. As histological structure is more readily appreciated in marsupial than most other mammalian enamels, owing to its tubularity, it was decided to make a brief examination of the enamel of young and old marsupials of the genus Macropus, for comparison with similarly made preparations of human enamel. Macropods were chosen because they exhibit the greatest degree of tubularity among marsupials. Sir John Tomes (1) in 1849 first described that tubular enamel occurs in marsupials and was “common to the teeth of at least the great majority of marsupials, if not all, except the wombat.” He also showed (2) that when it was decalcified the tubes could be seen maintaining their continuity with the dentine after the lime salts had been removed. He, too, first noted (1) that “in the human teeth the dentinal tubes are in small numbers, occasionally only continued for a short distance into the enamel,” and so drew attention to a resemblance between human and marsupial enamels at the amelo-dentinal junction. The observations of J. H. Mummery (3) in 1914 confirmed this.