IX] OF SOLUBILITY IN COLLOID MEDIA 669 



cipitates within the organism*. It has been shewn, in the first 

 place, that the presence of albumin has a notable effect on the 

 solubility in a watery solution of calcium salts, increasing the 

 solubility of the phosphate in a marked degree and that of the 

 carbonate in still greater proportion; but the sulphate is only very 

 little more soluble in presence of albumin than in pure water, and 

 the rarity of its occurrence within the organism is accounted for 

 thereby. On the other hand, the bodies derived from the breaking 

 down of the albumins — their "catabolic'' products, such as the 

 peptones, etc. — dissolve the calcium salts to a much less degree than 

 albumin itself; and phosphate of lime is scarcely more soluble in 

 them than in water. The probabihty is, therefore, that the actual 

 precipitation of the calcium salts is not due to the direct action of 

 carbonic acid on a more soluble salt (as was at one time believed); 

 but to catabolic changes in the proteids of the organism, which 

 throw down salts that had been already formed, but had remained 

 hitherto in albuminous solution. The very shght solubiHty of 

 calcium phosphate under such circumstances accounts for its pre- 

 dominance in mammalian bonef; and, in short, wherever a supply 

 of this salt has been available to the organism. 



To sum up, we see that, whether from food or from sea-water, 

 calcium sulphate will tend to pass but little into solution in the 

 albuminoid substances of the body: that calcium carbonate will 

 enter more freely, but a considerable part of it will tend to remain 

 in solution: while calcium phosphate will pass into solution in 

 considerable amount, but will be almost wholly precipitated again 

 as the albumin becomes broken down in the normal process of 

 metabolism. We have still to wait for a similar and equally 

 illuminating study of the solution and precipitation of silica in 

 presence of organic colloids. 



When carbonate of hme is secreted or precipitated by hving 

 organisms, to form bone, shell, egg-shell, coral and what not, its 

 mineralogical form may vary, but the causes which determine it 



* W. Pauli u. M. Samec, Ueber Loslichkeitsbeeinfliissung von Elektrolyten 

 durch Eiweisskorper, Biochem. Zeitschr. xvii, p. 235, 1910. Some of these results 

 were known much earher; cf. Fokker in Pflilger's Archiv, vii, p. 274, 1873; also 

 Robert Irvine and Sims Woodhead, op. cit. p. 347. 



t Which, in 1000 parts of ash. contains about 840 parts of phosphate and 

 76 parts of calcium carbonate. 



