36 THE TEETH. 



vations, that the skeleton of a pig increases on an average about 

 11 '7 grammes in weight daily during the first eight months after 

 birth ; that is to say, that about 6 '2 grammes of cartilage are daily 

 formed, and 5*5 grammes of earths (including 2*4 grammes of phos- 

 phoric acid) are taken up by the bones. At a subsequent period, as, 

 for instance, till the eleventh month, the skeleton increases on an 

 average about 6 grammes daily, that is to say, there are only about 

 2*6 grammes of earths (including 1*4 grammes of phosphoric acid) 

 deposited daily in the bones. 



THE TEETH. 



THE teeth have commonly been considered, in a chemical 

 point of view, as organs possessing very great analogy with the 

 bones, and they have been regarded as purely mechanically acting 

 parts, rich in mineral substances, and analogous to the products of 

 inorganic nature in short, to minerals ; but this mode of inves- 

 tigating the subject cannot satisfy the requirements of the histo- 

 logist or the physiologist. Independently of their mode of 

 development, the structure of the teeth differs so entirely from 

 that of the bones, and is moreover so complicated, that it would 

 be wholly irrational to regard the teeth as formed of homogeneous 

 simple tissues, and to submit them directly to chemical analysis. 



When we analyse an entire tooth, we are guilty of the same 

 error as the chemists of an earlier age who triturated complicated 

 organisms in a mortar, and then attempted to analyse the 

 chaotic mass. Even in a chemical investigation of the teeth, 

 we should remember that every tooth consists of three morpho- 

 logically different parts, namely, the dentine or tooth-substance, the 

 enamel, and the cement. 



The predominant part of the tooth, and that on which its form 

 depends, is the dentine (substantia tubulosa), a fusiform or wedge- 

 like body, provided with a club-shaped hollow extremity for the 

 reception of the nerves and nutrient vessels. Histological investi- 

 gation has shown that dentine is not a homogeneous body, but that 

 it consists of a perfectly structureless* mass, resembling the matrix 

 of bone, and perforated by a very large number of minute ramify- 



[* In the previous edition Lehmann says "not perfectly structureless." 

 According to Kolliker, the matrix of the dentine in the recent tooth is quite 

 homogeneous. After the extraction of the calcareous salts from the dentine, it, 

 however, exhibits a great tendency to break up into fibres. G. E. D.] 



