CALCIUM PHOSPHATE AND CALCIUM CARBONATE. 281 



i. That the salts are deposited in the matrix by a precipitation 

 in situ from the interaction of soluble salts in the blood and the 

 tissue. 



2. That the salts are excreted, or secreted, either with the matrix, 

 or into the matrix, by the bone cells. 



3. That a complex combination salt known as calcium carbono- 

 phosphate, carried in solution in the blood, is thrown out of solution 

 in the bony matrix by a change in the carbon dioxide content of 

 the tissue, and after precipitation is finally converted into the two 

 components, calcium carbonate and neutral calcium phosphate, in 

 the exact proportions found in bone. 



The weight of evidence is at present in favor of the third view, 

 especially supported by the work of Barille and of Wells, but it 

 seems to me that fully conclusive proof that this is the process has 

 not yet been brought forward. 



The precipitation theory, however, offers a very simple and 

 plausible explanation, and so it was determined to investigate the 

 behavior of bone salts on precipitation and see if any light could 

 be shed on the actual manner of impregnation of the bony matrix. 



An exact knowledge of the way in which the bone salts are added 

 would be a great aid, indeed, to our understanding of the growth 

 of bone, repair of fractures, changes in rickets and osteomalacia, 

 and other kindred conditions. It would also throw light on the 

 formation of calcareous patches in scar tissue and in arterioscle- 

 rosis, for Wells has shown that calcification and ossification are 

 quite similar processes, and the same two calcium salts are present 

 in both cases in exactly the same proportions. 



This research work, as finally carried out, involved the micro- 

 scopic study of the reactions whereby calcium carbonate and cal- 

 cium phosphate were precipitated, both in separate solutions and 

 also in the same solution, first in various aqueous media and then 

 in certain colloidal ones. This was followed by a thorough exam- 

 ination of the unchanged matrix of many different bones in the 

 mouse, the frog, the guinea pig, the dog, and human foetuses of 

 various ages. 



"For experimental investigation of the artificial process will 



