^ A MANUAL OF PHYSIOLOGY 



called plasmine of Denis on being dissolved in a little water, 

 does form a clot. Fibrin is therefore derived from some- 

 thing in this precipitate. Now, ' plasmine ' contains two 

 proteid bodies fibrinogen, which coagulates by heat at 

 about 56 C., and serum- globulin, which coagulates at about 

 75 C., and it was at one time believed that both of these 

 entered into the formation of fibrin (Schmidt). Hammer- 

 sten, however, has shown that fibrinogen alone is a precursor 

 of fibrin ; pure serum-globulin neither helps nor hinders 

 its formation. This observer isolated fibrinogen from blood- 

 plasma by adding sodium chloride till about 13 per cent, 

 was present. With this amount the fibrinogen is precipi- 

 tated, while serum-globulin is not precipitated till 20 per 

 cent, of salt is reached. After precipitation of the fibrinogen 

 the plasma no longer coagulates ; and a solution of pure 

 fibrinogen can be made to clot and to form fibrin, while a 

 solution of serum-globulin cannot. Blood-serum, too, which 

 contains abundance of serum-globulin, but no fibrinogen, 

 will not coagulate. 



So far, then, we have reached the conclusion that fibrin is 

 formed by a change in a substance, fibrinogen, which can be 

 obtained by certain methods from blood-plasma. It may 

 be added that there is evidence that fibrinogen exists as 

 such in the circulating blood ; for if unclotted blood be 

 suddenly heated to about 56, the temperature of heat- 

 coagulation of fibrinogen, the blood loses its power of 

 clotting. Since fibrinogen is readily soluble in dilute saline 

 solutions and fibrin only soluble with great difficulty, we 

 may say that in coagulation of the blood a substance soluble 

 in the plasma passes into an insoluble form. But this is 

 not a mere physical change, for it seems to be initiated by a 

 splitting up of the fibrinogen into two proteid bodies 

 thrombosin and fibrinoglobulin only the former of which 

 is transformed into fibrin, while the latter remains in solution. 



How is this change determined when blood is shed ? We 

 have said that a solution of pure fibrinogen can be made to 

 coagulate, but it does not coagulate of itself. The addition 

 of another substance in extremely minute quantity is neces- 

 sary. This other substance is fibrin ferment, which can be 



