104 MICROSCOPIC ANATOMY OF THE TEETH 



to prevent the disturbance and washing away of the dissolv- 

 ing enamel which usually occurs in these experiments, 

 a residue, indestructible by acids, is left which retains the 

 form and arrangement of the calcified tissue faintly 

 indicated on the slide. In the author's experiment a thin 

 ground section of the enamel and dentine of the Kangaroo 

 (Macropus rufus) was stained with toluidin blue and 

 placed in a drop of Farrant's solution on a microscope 

 slide. Strong hydrochloric acid was added drop by drop to 

 the Farrant solution and the action watched under the 

 microscope. No cover-glass was used and the specimen 

 was not disturbed by the action of confined bubbles of gas. 

 Decalcification proceeded very rapidly, and, when all the 

 calcified enamel had disappeared, the tubes were seen lying 

 in a faintly -tinted fibrillar stroma and had retained their 

 positions as in the formed tissue. The whole contour of 

 the piece of enamel could be traced upon the slide, and the 

 tubes were so little disturbed that their characteristic bending 

 in parallel lines near the dentine, so commonly seen in the 

 enamel of Macropus, was quite evident. The decalcification 

 experiment described by Sir John Tomes was carried out 

 in a watery medium and the delicate stroma was not retained 

 as in the dense medium employed by the author, but he was 

 able to demonstrate that the tubes passing from the dentine 

 to the enamel retained their form and could be seen waving 

 about in the acid solution. 



Further evidence of the delayed or only partial disappear- 

 ance of the organic basis of marsupial enamel is also seen 

 in the stained preparations of the completed tissue. As 

 shown in fig. 53 B, in many places the stain has penetrated 

 from the interprismatic spaces into a delicate fibrillar 

 structure within the matrix of the enamel ; this would 

 appear to be a portion of the organic basis which has escaped 

 calcification and has taken the stain as freely as the inter- 

 prismatic spaces themselves, which certainly in Macropus 

 appear from their staining reaction to have undergone in 

 many places very little or no calcification. 



Enamel of The enamel of Hyrax (the biblical Coney) is very com- 



yrax. pi e t e ly penetrated by tubes from the dentine which pass in 



many places all across it to the outer margin. At the June- 



