THE COAGULATION OF THE BLOOD. 371 



of small shreds of " washed blood-clot " caused the forma- 

 tion of fibrin in them. This power was exhibited to a still 

 greater extent by the " buffy coat " of a clot ; he therefore 

 concluded that the power resided in the white blood cor- 

 puscles which are so abundant in the buffy coat, and with 

 almost prophetic instinct, though he did not employ the 

 term ferment, he compared this action to the action of 

 rennet in curdling milk. 



British investigators having cleared the way, we find 

 the next important names among the workers on the 

 Continent. First came Denis, who saturated blood plasma 

 with sodium chloride, and thus obtained a proteid precipi- 

 tate. This precipitate was collected, re-dissolved in a little 

 water, and allowed to stand. The aqueous solution re- 

 mained liquid for a short time, but soon a clot of fibrin made 

 its appearance. Denis had thus obtained from the plasma 

 the soluble precursor of the insoluble fibrin, and he named 

 it plasmine. Denis' plasmine was soon shown to be a 

 mixture of at least three substances, and to them the term 

 fibrin-factors was, until quite recently, universally applied. 



Alexander Schmidt, Professor at Dorpat, recognised 

 these three materials and named them fibrinogen, fibrino- 

 plastin, and fibrin-ferment. He considered that the two 

 first-named substances, which belong to the globulin class 

 of proteids, united together and formed fibrin, and the 

 agency which caused their union was the fibrin-ferment. 



Olaf Hammarsten, of Upsala, ascertained the characters 

 of these substances with greater exactness, but his most 

 important contribution to science was the discovery that the 

 fibrinoplastin (or, as it is now called, paraglobulin or serum- 

 globulin) was not essential. A solution of fibrinogen plus 

 ferment will cause the formation of fibrin : the paraglobulin 

 always remains, if present, in solution, though its presence 

 hastens coagulation ; this faculty it was found to share in 

 common with casein from milk, and even the inorganic salt 

 calcium chloride. 



The question of the causation of blood clotting had now 

 narrowed itself still more. It was fibrin-ferment which 

 caused fibrin formation ; the cause of the formation of 



