58 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



after the blood is shed. The nucleo-albumio part is derived faom the cor- 

 puscles of the blood (leucocytes, blood-plates), which break down and go into 

 solution. This nucleo-albumin then unites with the calcium salts present in 

 the blood to form fibrin ferment, an organic compound of calcium capable of 

 reacting with fibrinogen. The theory is a simple one ; it accounts tor the 

 importance of calcium salts in coagulation, and reduces the interchange be- 

 tween fibrinogen and fibrin ferment to the nature of an ordinary chemical 

 reaction; but it cannot be accepted without reservation at present, since the 

 experimental evidence is not entirely in its favor. Hammarsten, for instance, 

 in some careful experiments seems to have obtained facts that are at variance 

 with a part at least of this theory. Hammarsten 1 states that blood-plasma 

 or fibrinogen solutions to which an excess of potsssium oxalate had been 

 added, and which therefore was free presumably from precipitable calcium 

 salts, underwent typical coagulation when mixed with blood-serum to which an 

 excess of oxalate had also been added. In other words, a solution of fibrinogen 

 free from calcium reacted with a solution of fibrin ferment (blood-serum) also 

 apparently free from calcium. It might be urged against this experiment, 

 however, that in the blood-serum used the combination of calcium and nucleo- 

 proteid to form ferment had already taken place, and that in this combination 

 the calcium is not acted upon by the oxalate. Hammarsten indeed admits that 

 something of this kind may occur, for he is convinced, like others, that calcium 

 in some way is essential to coagulation, his suggestion being that it plays an un- 

 known part in the formation of the ferment. He supposes that in the plasma 

 of shed blood a material is present which he designates as prothrombin, and 

 the calcium in some way converts this into the active ferment, the thrombin. 

 According to the more explicit hypothesis of Pekelharing, the prothrombin is 

 a form of nucleo-proteid and the thrombin a calcium compound of this pro- 

 teid. The second part of IVkelharing's theory, namely, that the reaction 

 between the ferment and the fibrinogen consists in a transfer of the calcium 

 from the former to the latter, is directly contradicted by Ilammarsten's experi- 

 ments. Quantitative analysis of fibrinogen and fibrin showed that the latter 

 docs not contain any larger amount of calcium than the former. This author 

 is inclined to consider the ( a contained in fibrin of the nature of an impurity, 

 and not as an essential constituent of the fibrin molecule. By the use of 

 special methods he has succeeded in obtaining typical fibrin containing as 

 little as 0.005 per cent, of ('a. We must be content to say that in the clot- 

 ting of blood three factors are necessary — namely, the fibrinogen and the 

 calcium salts of plasma, which are present in the circulating blood, and the 

 fibrin ferment, which is formed after the blood is shed. 



Nature and Origin of Fibrin Ferment (Thrombin). — Recent views as 

 to the nature of fibrin ferment have been referred to incidentally in the 

 description of the theories of coagulation just given. The relation of these 

 newei' views to the older idea- can be presented most easily by giving a 

 brief description of the development of our know ledge concerning this body. 

 1 Zeitschriftfiir physiologische Chemie, Bd. -:-2. S. 333, and 1899, Bd. 28, S. 98.' 



