22 METABOLISM OF ORGANIC AND INORGANIC PHOSPHORTS. 



found from fifteen to twenty times as much calcium in the blood as in 

 normal health. More calcium is absorbed from natural food than 

 from artificial, and in the latter case more calcium is likely to be ex- 

 creted by the bowels unaltered than normally. The amount of cal- 

 cium retained b} r the tissues and its manner of combination depend 

 both upon the quality of the food and the amount of calcium in it 



With the exception of the importance* of the alkaline earths as 

 carbonates, and especially as phosphates, on the physical composition 

 of certain structures, such as the bones and teeth, their physio- 

 logical importance is nearly unknown. The occurrence of earthy 

 phosphates in all proteins, and their great importance in the passage 

 of the proteins from a soluble to a coagulable state, make it probable 

 that the earthy phosphates play an important part in the organiza- 

 tion of the proteins. An insufficient supply of alkali earths in the 

 food raises an interesting question as to the effect of this lack on the 

 bony structure. 



CALCIUM SALTS AND COAGULATION. 



The property which is the most characteristic of casein is that it 

 coagulates with rennet in the presence of a sufficiently great amount 

 of lime salts. In solutions free from lime salts the casein does not 

 coagulate with rennet, but if lime salts are added it is changed so that 

 the solution (even if the enzym is destnyyed b} 7 heating) yields a 

 coagulated mass, having the properties of curd. 



According to Soxhlet a the soluble lime salts are only of essential 

 importance in coagulation, wliile the calcium phosphate is without 

 importance. According to Courant 6 the calcium casein compound 

 on coagulation may cany down with it, if the solution contains di- 

 calcium phosphate, a part of this as tricalcium phosphate, leaving 

 monocalcium phosphate in the solution. The chemical process wliich 

 takes place in the rennet coagulation has not been thoroughly investi- 

 gated. 



The fibrin ferment, wliich was called thrombin by Schmidt, is pro- 

 duced, according to Pekelharing, d by the action of soluble calcium 

 salts on a preformed zymogen existing in the noncoagulated plasma. 

 Schmidt admits the presence of such a mother-substance of fibrin 

 ferment in the blood and calls it prothrombin. 



Briicke* showed long ago that fibrin left an ash containing calcium 

 phosphate. The fact that calcium salts may facilitate or even cause 

 a coagulation in liquids poor in fibrin ferment has been known for a 



Munch, med. Wochenschr., 1893, 40 : 61. 



& Arch, gesam. Physiol., 1891, 50 : 109. 



c Zur Blutlehre, Leipzig, 1892. 



<*Zts. physiol. Chem., 1896-7, ..'.' : 245. 



Vorlesungen tiber Physiologic, 2nd ed., 1875, 1 : 270. 



