304 JAMES CRAWFORD WATT. 



a fibrous character, and this then has the calcium salts deposited 

 in it. 



The final possible explanation of the deposit of bone salts in 

 the matrix is the secretory one. Wells and others have been forced 

 to the conclusion that there is a selective or specific action of tis- 

 sues, such as cartilage or membrane about to ossify, by which 

 calcium salts are absorbed or otherwise taken into them, while 

 apparently entirely similar areas of cartilage and membrane do not 

 ossify at that time or at any later time. From this view of selective 

 action it is not a far step to that of secretory action, explaining 

 the ossifying process as a secretion of the calcium salts by the bone 

 forming cells. It is already generally admitted that the matrix is 

 a product of the bone cells, and if this is true, it is quite logical 

 to assume that the calcium salts are taken by the bone cells from 

 the blood and passed on into the matrix. 



The difficulty in this theory has been to account for the amount 

 of phosphate in the tissues. The calcium was looked upon as 

 being derived from that carried in the blood, but the phosphate was 

 explained as being due to cellular activities, derived either from 

 the nucleus or from cellular degeneration. Another difficulty here, 

 again, is to explain the fixed ratio of carbonate and phosphate. 

 This, of course, could be looked upon as due to the carbon dioxide 

 content of the tissue, or as due to the activity of the cell, a definite 

 proportion being found in the secretory products here just as in 

 other organs of the body. 



It seems to me, however, that the nearest approach to the truth 

 is to be obtained by combining two views. The bone salts, I be- 

 lieve, reach the tissue as the soluble double salt, tribasic calcium 

 carbonophosphate, which by its constitution provides for the tissue 

 both calcium carbonate and calcium phosphate, each salt in the 

 proper proportion found in bone. I do not believe, however, that 

 deposit here is by precipitation, for in the bone, owing to the col- 

 loidal matrix, the hydrogen-ion concentration, and the presence of 

 lecithin, all conditions are most favorable to a visible and char- 

 acteristic precipitate, showing granules and spherules, but there is 

 no visible evidence whatever of these bodies. The only evidence 

 in favor of precipitation consists of the following two sets of facts : 



