ENAMEL 103 



fibres, and he states that one could see by such experiments 

 that the floating tubes are isolated twisted objects and are 

 not held together by any membrane. In the author's 

 decalcification experiment to be presently described, a 

 distinct fibrillar basis to the enamel remained, in which 

 these tubes lay. 



From an examination of his own stained preparations 

 the author considers there can be no doubt that the tubes 

 lie between and not within the prisms. Professor Von Ebner 

 and Professor Paul both consider that the tubes lie between 

 the prisms, but C. S. Tomes looks upon the tubes of 

 marsupial enamel as canals in the centre of the prisms, 

 considering that calcification in marsupial and other mam- 

 malian enamels takes place centripetally, leading in some 

 cases to the complete obliteration of the central channel as 

 in human teeth, in others not reaching the centre and so 

 leaving tubes within the prisms ; there is a squeezing up, 

 as it were, of the central canal by the. advancing calcification. 

 According to this view there would be no true interprismatic 

 substance in enamel, calcification with regard to the prisms 

 proceeding from without inwards. The tubes in the enamel 

 of marsupials are, he considers, entirely a product of the 

 enamel organ and cannot properly be called dentinal tubes, 

 and their connexion with the dentinal tubes he would look 

 upon as a joining up of the enamel tubes with those of the 

 dentine. 



One cannot but consider, however, that the evidences 

 given by finished structure and development are very 

 strongly in favour of the existence of a very distinct inter- 

 prismatic substance, and further corroborative evidence 

 has lately been advanced in the paper by the late Dr. Black 

 on the curious endemic disease of the teeth in the Rocky 

 Mountains above referred to, where the interprismatic 

 substance appears to be the sole part of the enamel affected 

 (see p. 71). 



It would appear that the organic basis of marsupial 

 enamel is more persistent than that of the enamel of the 

 higher mammalia. 



If a piece of a ground section of marsupial enamel and 

 dentine is decalcified on a slide, with suitable precautions, 



