INTRODUCTION. xlix 



dentine no trace of the blood vessels remains ; all has been con- 

 verted into a much more minute calcified tubular tissue by the 

 assimilative or intus-susceptive properties of cells, and by the modi- 

 fication of their nucleolar contents. (1) 



(1) That the dentine is the ossified pulp is, as Dr. Schwann observes, an old opinion ; but 

 an opinion is not a theory. Almost every true theory has been indicated, with various degrees 

 of approximation, before its final estabUshraent ; but he has ever been held, in exact philosophy, 

 to be the discoverer of a theory, by whom it has been first clearly enunciated and satisfactorily 

 proved. Thus established, on the basis of careful and sound induction, it is sooner or later 

 received to the exclusion of the, till then, prevalent and generally accepted erroneous doctrine, 

 at which period the truth of the antecedent hints and indications of the true theory begins to 

 be perceived, and it is not uncommon to find their value exaggerated in quotations by the 

 emphasis of type. Thus the remark of Blake : — " As the bone of the tooth increases in 

 thickness, the pulp is proportionally diminished : and seems as it were converted into bone," 

 (Essay, 8vo. 1801, p. 7) is quoted in the article " Zoology," ' Encyclop. Metropclit.,' vol. vii, 

 p. 232, with " converted into hone" in italics. So also Mr. Conybeare's observation that the 

 interior cavity of the teeth of the Ichthyosaurus was obliterated "by the ossification of the 

 pulpy nucleus" ; and that " the ossified pulp has become a spongy mass of reticulated bony 

 fibres," (Geological Transactions, Second Series, vol. i, 1824, p. 107) might be cited in italics, 

 as the older hypothesis of Rau (De ortu et regeneratione dentium) has been, in depreciation of 

 the value or necessity of researches estabhshing the true relation of dentification to ossification. 

 But the actual value and bearing of such casual expressions would have been more fairly and 

 truly set forth, if, when the theory of the formation of dentine by successively excreted layers, 

 as promulgated by Hunter and Cuvier, universally prevailed in the systems of Physiology, 

 that theory had been formally combatted on the strength of such facts and observations in the 

 development of dentine, which it could be shown that Raw, Blake, Conybeare, and others, 

 had advanced in support of their expressions of the seeming, or actual conversion of the pulp 

 into bone. 



Such expressions are, however devoid of scientific value, in regard to the question 

 of development on which they are quoted to bear, precisely because they are unsupported by 

 the observations requisite to prove what they aflfirm, and they have, therefore, been deservedly 

 neglected by the best authorities in Physiology, who have treated ex professo on the develop- 

 ment of teeth, prior to 1839. 



In the edition of the English translation of "MifUer's Physiology" of 1837, many facts 

 are cited from Blake's excellent Treatise, but not his idea of the seeming conversion of tne 

 pulp into bone. The Translator, indeed, adds to She text the microscopic observations ot 



