DEVELOPMENT OF THE ENAMEL 169 



There are no doubt many objections to the above explana- 

 tion, and further researches are very desirable before we can 

 have a clear understanding of the exact chemical conditions 

 in calcification, but very considerable light has lately been 

 thrown upon this question by the researches of Pauli and 

 Samec (1910) (20), referred to by Professor D'Arcy Thompson 

 in his work on Growth and Form (25), from which the following 

 quotation is taken : ' It has been shown, in the first place, 

 that the presence of albumin has a notable effect on the 

 solubility in a watery solution of calcium salts, increasing the 

 solubility of the phosphate in a marked degree, and that of 

 the carbonate in still greater proportion ; but the sulphate 

 is only very little more soluble in the presence of albumin 

 than in pure water, and the rarity of its occurrence within 

 the organism is so far accounted for. On the other hand, 

 the bodies derived from the breaking down of the albumins, 

 their " catabolic " products, such as the peptones, &c., 

 dissolve the calcium salts to a much less degree than 

 albumin itself ; and in the case of the phosphate, its solu- 

 bility in them is scarcely greater than in water. The 

 probability is, therefore, that the actual precipitation of the 

 calcium salts is not due to the direct action of carbonic 

 acid, &c., on a more soluble salt (as was at one time believed), 

 but to catabolic changes in the proteids of the organism, 

 which tend to throw down the salts already formed, 

 which had remained hitherto in albuminous solution. The 

 very slight solubility of calcium phosphate under such 

 circumstances accounts for its predominance in, for instance, 

 mammalian bone, and wherever, in short, the supply of 

 this salt has been available to the organism. 



' To sum up, we see that, whether from food or from sea- 

 water, calcium sulphate will tend to pass but little into 

 solution in the albuminoid substances of the body ; calcium 

 carbonate will enter more freely, but a considerable part 

 of it will tend to remain in solution ; while calcium phosphate 

 will pass into solution in considerable amount, but will be 

 almost wholly precipitated again, as the albumin becomes 

 broken down in the normal process of metabolism.' l 



1 D'Arcy W. Thompson, Growth and Form, pp. 434 and 435. 



