CALCIUM PHOSPHATE AND CALCIUM CARBONATE. 307 



pass through the tissues is a most valuable one for the proper com- 

 prehension of some of the processes of growth, repair of fractures, 

 and changes going on in rarefaction of bony tissues. 



Summary. 



1. Calcium phosphate precipitated in water or in colloidal solu- 

 tions is constantly granular and amorphous in character, and 

 apparently uninfluenced by the nature of the solution. 



2. Calcium carbonate precipitated in water shows a great di- 

 versity of crystalline form ; in colloidal solutions it shows two main 

 forms, an irregular crystalline one and a spherical. 



3. Mixtures by simultaneous precipitation of both salts in the 

 same solution show each salt separating out independently and the 

 part of the deposit formed by each can be easily identified. 



4. Spherule formation by calcium carbonate is a typical reaction 

 in colloidal solutions. 



5. Spherules and crystals are influenced in shape, size, number, 

 and internal structure by a variety of substances found normally 

 or pathologically in the blood, most notably by lecithin which favors 

 the formation of large spherules, and by acetone which increases 

 the rapidity and extent of precipitation. 



6. The character of the deposit of calcium carbonate is influenced 

 by the hydrogen-ion concentration of the colloidal solution, being 

 most crystalline in acid media, all in the form of spherules in 

 strongly alkaline media, and mixed in form in solutions neutral or 

 nearly neutral. 



7. Large spherules, after persisting for months may undergo a 

 sort of degenerative process, with change of internal structure, 

 after which they dissolve and the material forming them is laid 

 down in a crystalline form. As far as I know this phenomenon 

 has never been previously described. 



8. In fresh bone of various animals examined in various ways 

 there is no visible microscopic evidence of the bone salts, although 

 they form two thirds of the mass of the matrix. The inference 

 is that the bone salts are not deposited in the matrix by simple 

 precipitation, for the conditions are such that, if precipitated, 

 granules, spherules, and crystals should be visible. 



