168 MICROSCOPIC ANATOMY OF THE TEETH 



fact it is hard to understand how the large spherites, which in 

 all outward appearance resemble the artificially produced 

 carbonate calcospherites, are produced. We see no altera- 

 tion of the spheroidal to the crystalline form, and when the 

 structure of finished enamel is revealed by the action of 

 caries and erosion the outlines of these large spherites can 

 still be traced. 



The question arises whether in the early stages of calcifica- 

 tion the carbonates preponderate ; but there are no analyses 

 of forming enamel, and they would be very difficult, if not 

 impossible, to obtain. 



Professor Sims Woodhead (29), however, suggests that 

 in the early stages of bone formation, which also shows an 

 excess of phosphates in the completed tissue, the carbonates 

 may be present in excess. He says, * Newly formed bones, 

 or new bone tissue of any kind, where the cells are extremely- 

 active in building up the matrix, almost invariably have 

 a larger proportion of carbonate of lime than fully formed 

 ones, because here the active cells set free a larger proportion 

 of carbonic acid, as a result of which more phosphoric acid 

 may be replaced by the carbonic acid lime salts '. The same 

 conditions probably apply to the other calcified organic 

 tissues of the body, as enamel and dentine. The conditions 

 in young growing animals, where the metabolic changes are 

 very active, are eminently favourable to the production of 

 carbonic acid, and it is quite conceivable, and in fact 

 probable, that in the early stages of enamel and dentine 

 formation the carbonates may be greatly in excess of the 

 phosphates, and thus the deposit of lime salts as calco- 

 spherites be better understood. 



As stated by C. S. Tomes, Hoppe-Seyler considers that the 

 salt in teeth and bone is a double salt, consisting of three 

 equivalents of calcium phosphate with one of calcium 

 carbonate. 



Whether in this combination the influence of the car- 

 bonate may be effective in causing a globular deposit might 

 be considered ; but in whatever way we explain the chemical 

 conditions which allow of their formation, we cannot escape 

 the evidence that in both dentine and enamel the lime 

 salts are deposited in the globular form. 



