THEIR HISTOLOGICAL RELATIONS. 3? 



ing canals. These canals have comparatively thick distinct walls, 

 and proceed from the cavities, diverging towards the external 

 surface of the dentine, in the vicinity of which they are still more 

 minutely ramified. We do not observe bone-corpuscles, or other 

 structures peculiar to bone, in the dentine ; but in their place we 

 have the interylobular spaces of Czermak,* which resemble the 

 holes made by bullets. We must, therefore, take into account 

 the contents of these tubes (probably the nutrient fluid of the 

 tooth), and of the above-named cavities, in the chemical investiga- 

 tion of the fresh teeth. It is clearly shown by microscopico- 

 mechanical examination, that here also the salts of lime are not 

 deposited in the canals or cavities. 



Hoppe f exposed to the prolonged action of boiling water thin 

 sections of the molar teeth of the pig, the salts having been pre- 

 viously extracted with hydrochloric acid, and the cartilage of the 

 cement having been removed with water. The external part swelled 

 up, became transparent, and dissolved, with the exception of a few 

 flakes; while, on the other hand, the interior became white and 

 transparent, crumbled down, and was scarcely at all soluble. The 

 solution only contained glutin. The undissolved residue, when 

 examined under the microscope, presented the dentinal canals in a 

 perfectly isolated state, and aggregations of dark globules with dis- 

 tinct nuclei : these globules perfectly corresponded with the above- 

 mentioned interglobular spaces. Acetic acid dissolved neither the 

 canals nor the globules. Hence, according to Hoppe, the canals, 

 like the bone-corpuscles, possess independent walls which do not 

 consist of a gelatigenous substance ; Hoppe considers the globules 

 to be cells. 



Slight as is the resemblance between dentine and osseous tissue 

 in a morphological point] of view, there is still less similarity 

 between the vitreous investment of the crown of the tooth (or the 

 enamel) and bone. The enamel is a very hard and rather brittle 

 compact mass, not permeated by canals or pores, and composed of 

 fibres resembling 4 or 6-sided prisms, diverging from the crown of 

 the tooth : whether these fibres (the so-called enamel prisms) are 

 agglutinated together by a special intermediate substance, is not 

 yet decided: a more accurate chemical investigation may probably 

 enable us to determine this point. 



According to Hoppe4 the enamel, after the extraction of its 



* Zeitsch, f. wiss. Zool. Bd. 2, S. 295-322. 

 t Arch. f. pathol. Anat. Bd. 5, S. 170-188. 

 J Op. cit. 



