136 PHYSIOLOGY CHAP. 



The presence of a certain amount of soluble and readily 

 ionisable lime salts in the plasma seems essential to coagulation, or 

 to the transformation of the soluble thrombosin into fibrin, which 

 precipitates as a clot. The reason why oxalates and sodium 

 fluoride, even in small doses, render plasma incoagulable lies in the 

 fact that they precipitate the calcium salts dissolved in the plasma, 

 and thus hinder the conversion of thrombosin into fibrin by 

 combination with the lime salts. Fibrin accordingly would be a 

 compound of calcium with thrombosin, and comparable as such 

 with the soluble curd which is a calcium compound of paracasein. 

 Just as milk casein splits under the action of the rennet ferment 

 into paracasein and a special albumose, so fibrinogen splits up 

 during blood coagulation, two-thirds of it forming thrombosin and 

 one-third fibrinoglobulin. As paracasein in combination with lime 

 forms curd, so thrombosin in the same combination produces 

 fibrin (Arthus, Lilienfeld). 



To this ingenious parallel between the clotting of blood and 

 that of milk, the objection has been raised that even if fibrin 

 always contains lime, it is no richer in lime than is the fibrinogen ; 

 hence it cannot be assumed that fibrinogen takes up lime from the 

 plasma in its transformations into fibrin. 



Others on the contrary affirm, perhaps more reasonably, that 

 coagulation is produced by a simple splitting of the fibrinogen into 

 a less soluble body that precipitates (fibrin), and another that is 

 soluble (fibrin globulin) which remains in the serum ; the presence 

 of lime seems indispensable, not to this reaction directly, but to the 

 production or the activity of the fibrin ferment. 



In any case it is undeniable that the presence of calcium in 

 plasma is essential to coagulation, even if its precise action is still 

 undetermined. 



(e} Another question to be solved relates to the chemical form 

 of the calcium when it participates as an indispensable factor in 

 coagulation. 



Some hold that it intervenes as a phosphate, more correctly as a 

 tricalcic phosphate, and think that as it is insoluble in water, it 

 remains dissolved in the plasma in combination with the proteins ; 

 Arthus, however, demonstrated that insoluble lime salts are useless, 

 and that the presence of soluble salts is essential. Sabbatani 

 further demonstrated that it is not merely the soluble salts, but 

 also the ionisable salts of calcium that are always present in plasma, 

 which are indispensable. 



It therefore appears probable that calcium intervenes in 

 coagulation in virtue of its characters and chemical properties as a 

 kat-ion, combining with those elements that have the function of 

 an-ions, perhaps with the leuconuclein of Lilienfeld, which we 

 shall discuss later. 



The quantity of calcium ions adequate to produce blood 



