140 MICROSCOPIC ANATOMY OF THE TEETH 



condition of suspension, the rounded contour of the liquid 

 form produced by surface tension is maintained, while 

 a process of crystallization tends to take place throughout 

 this little liquid globule. This is the explanation which has 

 been given of the first determination of the rounded forms 

 which occur in colloidal substances, and there are many 

 phenomena which point to the correctness of this view. 



The more recently investigated phenomena of adsorption 

 which are intimately associated with surface tension no 

 doubt take an important part in the processes of calcifica- 

 tion in the living body. 



These phenomena depend upon the power of the adsorbed 

 substance to lower the surface tension, and itself accumu- 

 lating at the surface it leads to the formation of membranes, 

 and bears an intimate relation to the phenomena of osmosis. 1 



Both Rainey and Harting found that when calcium 

 phosphate was present in the solutions in excess of the 

 carbonate, globular bodies were not formed, but the deposit 

 was crystalline, but if there was only a small proportion of 

 phosphate to carbonate, larger and more perfect spheres 

 were produced than with carbonate alone. This observation 

 has a most important bearing on the subject of the calcifica- 

 tion of the hard tissues of the teeth, as in completed dentine 

 and enamel the phosphates are largely in excess ; but this 

 question will be further considered in discussing the calcifica- 

 tion of enamel. 



In the works of Harting and Rainey a full and minute 

 description is given of the various forms in which the calcific 

 matter is deposited. 



Two main forms of calcospherites may, however, be con- 

 veniently distinguished those in which radial striae are 

 most evident and those especially marked by concentric 

 lamellae or rings, although there are many which show both 

 structures. In developing enamel it will be shown that the 

 deposited spherites belong to the radial system, while in 

 dentine they are of the concentric form (fig. 80). 



1 For a further study of the phenomena of adsorption the following works 

 may be consulted : D'Arcy W. Thompson, Growth and Form, p. 277, &c. ; 

 Bayliss, Principles of General Physiology, pp. 54-73 ; Taylor's Chemistry 

 of Colloids, p. 221, &c. ; and W. Ostwald, Grundriss der Kolloidchemie (1909). 



