PHYSIOLOGY. 



The clotting of the blood is due to the development in it of 

 fibrin, whose fibrils arrange themselves in the form of a network. 



In blood within its vessels there are found no such fibrils of 

 fibrin; therefore normally no coagulation occurs within the body. 

 These fibrils then must have been formed by some change, chemical 

 or otherwise, of one or more constituents of the blood. That the 

 corpuscles themselves cannot form a clot excludes them, so that our 

 attention is turned to the plasma. In it is formed the fibrin, for 

 pure plasma from which the corpuscles have been removed very 

 readily coagulates. When blood is vigorously beaten with twigs, 

 long shreds of a nearly transparent substance are found adhering 

 to them. These are fibrin-fibers, free, or nearly so, from corpuscles. 

 Its structure consists of very delicate, doubly-refractive fibrils of 

 microscopical size. 



Many theories have been propounded to account for the forma- 

 tion of fibrin and the coagulation of the blood, but the one most 

 widely received is that of Hammersten, a Swedish investigator. 



In the study of plasma it was learned that one of its constitu- 

 ents was a proteid of the globulin class, to which had been given 

 the name fibrinogen. It is held in solution by the plasma and is 

 believed to be an end-product of the disintegration of useless white 

 corpuscles. Within the circulating fluid there is an immense num- 

 ber of these white cells; when blood is withdrawn from the living 

 vessel there is a large and very sudden destruction of them ; accord- 

 ing to Alexander Schmidt, 71.7 per cent, are dissolved. When these 

 little bodies are disintegrated in the laboratory they yield nucleo- 

 proteids; so that it is very probable that practically the same 

 products result upon disintegration in the shed blood. To this 

 nucleo-proteid has been given the name prollirombin. By the action 

 of the calcium salts dissolved in the blood-plasma the prothrombin 

 is converted into fibrin-ferment, or tlirombin. When thrombin comes 

 into contact with the fibrinogen molecule dissolved in the plasma it 

 splits it into two parts: one is a globulin, which is very small in 

 proportion and equally unimportant; it remains in solution. The 

 other is the insoluble substance fibrin, which entangles the corpus- 

 cles and is so essential to the formation of the blood-clot. 



To epitomize, it may be said that coagulation depends upon 

 three factors, according to Hammersten's theory : (1) calcium salts to 

 convert the nucleo-proteids in the form of prothrombin into tlirom- 

 lin, or (2) fibrin-ferment; this latter breaks up the (3) fibrinogen in 

 solution into an unimportant globulin and the all-important fibrin. 



