302 JAMES CRAWFORD WATT. 



Rainey and by Biedermann. The dentine and enamel of the teeth, 

 Rainey believed he had demonstrated to be composed of spherules, 

 forming in rows and coalescing. Neither in old bone nor in new, 

 nor in a transitional area transforming from cartilage to bone, have 

 I seen either a single crystal or a single spherule. 



Previous work has demonstrated that spherules can always be 

 found in calcium carbonate precipitated in colloids. This forma- 

 tion is favored by the occurrence of the reaction gradually and 

 slowly, and also by the presence of lecithin, which is found in both 

 blood and bone, so that all the conditions in the matrix of the bone 

 are favorable to the formation of spherules if precipitation occurs. 

 The hydrogen-ion concentration is also favorable to formation of 

 large spherules. With optimum conditions for their occurrence, 

 and with a complete absence of these bodies, the interpretation is 

 that the salts found in the bony matrix are not deposited in it by 

 simple precipitation from a double decomposition of Salts in the 

 blood or the tissue. This is purely negative evidence, which, of 

 course, is not of the same value as positive evidence, but it seems 

 to me forms a very strong point against the simple precipitation 

 theory. 



It must be noted, however, that if calcium carbonate is very 

 small in amount compared to the amount of phosphate precipitated 

 that spherules may not be in evidence, but the whole precipitate 

 will be granular, with coarser granules, resembling minute spher- 

 ules and interpreted as carbonate interspersed among the masses 

 of finer granules formed by the phosphate. It must be empha- 

 sized that homogeneous masses such as seen in the bony matrix 

 never occurred in any of my experiments, but precipitates, no mat- 

 ter how long they were kept, remained composed of distinct dis- 

 crete particles. 



Another point against this theory is that it supposes that a 

 soluble salt of calcium circulates in the blood to be precipitated as 

 phosphate and carbonate in the bone. With the large amount of 

 sodium carbonate and sodium phosphate in the blood, calcium car- 

 bonate and phosphate should be formed at once, here and not in 

 the bone. But calcium is present in the blood in a greater amount 

 than calcium carbonate and calcium phosphate are soluble in water. 



