CALCIUM PHOSPHATE AND CALCIUM CARBONATE. 289 



stances very remarkable changes of form resulted. The influence 

 oh calcium phosphate was much less striking, as this deposit re- 

 mained in the same granular, amorphous form in all cases, and the 

 results were mainly a slight difference in the average size of 

 granules, and also differences in the speed and completeness of 

 precipitation similar to those which will be noted in detail below 

 for calcium carbonate, to which latter deposit alone the succeeding 

 paragraphs relate. 



Addition of Sodium Chloride. 



The main effect noted on adding sodium chloride was the speed- 

 ing up of the reaction. Brownian movement ceased sooner, crys- 

 tallization was more rapid, and in most cases the main portion of 

 the precipitate consisted of smaller crystals and spherules, and in 

 the colloids the crystals were of very poor shape. 



Addition of Dextrose. 



The influence of this compound was slight and seemed to consist 

 mostly in added transparency of the crystals and spherules. There 

 was also slight modification in shape. 



Addition of Urea. 

 Even in aqueous solutions some spherules were formed when 

 urea was present. The effect in colloidal solution (Figs. 30 and 

 35) was to favor increase in size of the spherules, with a marked 

 tendency toward fusion, so that many double forms and dumbbell- 

 shaped bodies were seen. Urea thus shows an influence quite the 

 opposite of sodium chloride upon the precipitate. It evidently 

 favors growth of this deposit and suggests the idea that the pres- 

 ence of urea in blood and in urine may aid in the deposit of calcium 

 salts in the calcareous incrustation of sclerotic arteries and the 

 growth of renal and vesical calculi. 



Addition of Lecithin. 



Lecithin, even in small amounts, 0.1 gm. in 100 c.c. water gives 

 a turbid solution even after filtering, but microscopically the solu- 

 tion appears clear, so that it is evidently a colloidal one. 



The lecithin has a remarkable influence on the precipitation of 



