268 COLLOIDS IN BIOLOGY AND MEDICINE 



Ossification Processes. 



One of the most interesting of colloid-chemical problems is bone 

 formation. We shall see on page 302 that from an aqueous solution 

 containing blood salts, calcium carbonate and calcium phosphate 

 precipitate. The precipitation is hindered by the presence of the 

 blood colloids, though two-thirds of Ca salts, at least in the serum of 

 higher animals, occur in the crystalloid state. This interference 

 must stop during the formation of bone. To account for this there 

 are several theoretical possibilities : it may be assumed that changes in 

 the serum colloids are brought about at or from the bone cells, which 

 remove their protective action and results in the precipitation of the 

 calcium salts. This agrees with the views of Wo. PAULI and SAMEC,* 

 which we shall consider more closely. It was shown in their researches 

 that the increase in the solubility of calcium carbonate by serum 

 albumin was 475 per cent, and of calcium phosphate 90 per cent. We 

 would consequently expect to find a very much more extensive pre- 

 cipitation of calcium phosphate than of calcium carbonate when the 

 protective action was removed. But in the case of bones, the pro- 

 portions are just the reverse. The bone ash of man contains about 

 850 parts Ca 3 (PO 4 ) 2 and 90 parts CaCO 3 per 1000. 



But in the case of a cleavage product of albumin, Wo. PAULI 

 and SAMEC found that the solvent action upon calcium salts was 

 the reverse. Witte's peptone, consisting almost entirely of albumoses, 

 holds in solution only the calcium carbonate, whereas the calcium 

 phosphate exhibits a diminution in solubility. Based on these 

 results, ossification might occur in the following way : In the bone or 

 cartilage cells, there occurs a concentration of colloids in which a 

 large quantity of calcium salts are piled up. When these tissue col- 

 loids are broken down, a precipitation occurs, the precipitate consist- 

 ing chiefly of calcium phosphate with smaller amounts of calcium 

 carbonate. This corresponds with the histological evidence, by means 

 of which a tissue destruction may be seen to accompany ossification. 



A further possibility, which does not in the least contradict the 

 above explanation but possibly coincides with it, is that phosphates 

 are set free and come into contact with the carbonates always 

 present when the tissues, especially the cell nuclei, break down. In 

 accordance with well-known physico-chemical laws, an increase in the 

 concentration of an ion (in this case the phosphate ion) results in an 

 increase in the calcium phosphate molecules, and this changed albumin 

 must, accordingly, favor the precipitation of calcium phosphate. 



Finally we may think of a kind of specific adsorption by certain 

 cell groups. In fact, M. PFAUNDLER noticed a selective adsorption of 



