182 MICROSCOPIC ANATOMY OF THE TEETH 



through the kindness of Dr. M. Cryer of Philadelphia he 

 was able to obtain material prepared in this manner, which 

 gave very satisfactory results, and he ventures to think, 

 shed an entirely new light on the process of calcification 

 in certain fish. 



From the preparations of Sargus germs which he did 

 obtain, Tomes considered that the process was in all essen- 

 tials the same as in the Gadidse. It is, however, very evident 

 from a study of the author's sections that the process is not 

 the same as described by Tomes in the Gadidse. 



The dental germs of fish are so very delicate that the 

 ordinary treatment with alcohol and paraffin is quite inappli- 

 cable to them. 



Specimens hardened in formol were decalcified in formic 

 acid, embedded in gum solution, and cut in the freezing 

 microtome. The use of alcohol at any stage was avoided, 

 and the specimens were mounted, after staining, in Farrant's 

 medium. Some specimens of Sargus made in the ordinary 

 manner and embedded in paraffin showed that in early 

 stages there is a distinct layer of ameloblasts and an external 

 epithelium as in the Gadidse, and that a layer of enamel had 

 been deposited under the influence of the ameloblasts. 



Later germs showed the apparent disappearance of the 

 ameloblasts as in Gadidse, but although a stroma was seen 

 with parallel strise their structure was very indefinite, and 

 while there were indications of the presence of blood-vessels 

 in the enamel organ they could not be clearly distinguished. 

 The frozen sections, however, showed that the earlier ones 

 were badly shrunk from the treatment with heat and 

 alcohol, and gave a very different appearance. 



In these sections there is a very clearly defined capsule 

 with abundant blood-vessels, and a structure is seen between 

 the capsule and the forming enamel which is arranged in 

 parallel lines at right angles to the surface, and does not 

 quite reach the forming enamel, from which it is separated 

 by a narrow band of delicate reticular tissue (fig. 100). 

 An examination of these parallel strise shows that they are 

 made up of blood-vessels in direct continuation with those of 

 the capsule, regularly alternating with an apparently tubular 

 substance with concave margins (figs. 101 and 103). Between 



