356 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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

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

 reaction. 



Lilienfeld's Theory of Coagulation. Lilienfeld ' has carried still further the 

 chemical study of the changes occurring in coagulation. Like Pekelharing 

 he finds that the three important substances to be considered in coagulation 

 are fibrinogen, nuclein compounds, and calcium salts. He differs from Pekel- 

 haring, however, in his description of how these substances react with one 

 another in producing fibrin. Lilienfeld and others have shown that a com- 

 pound proteid to which the name " nucleohiston " is given may be extracted 

 from the nuclei of leucocytes and other cells, and that this neucleohiston under 

 some circumstances favors the coagulation of liquids containing fibrinogen, but 

 under other circumstances prevents or retards coagulation. Nucleohiston is 

 readily decomposed into its two constituents histon, a proteid body, and a 

 nucleo-proteid to which the specific name of " leuconuclein " is given. Histon 

 when injected into the blood of a living animal has a remarkable influence in 

 preventing coagulation : blood drawn shortly after the injection remains per- 

 fectly fluid, and its histological elements, red and white corpuscles and blood- 

 plates, retain perfectly their normal shapes. Leuconuclein, on the contrary, 

 although it is not able to produce fibrin from fibrinogen, does cause the fibrin- 

 ogen molecule to split, with the formation of a substance, " thrombosin," 

 which comes down as a precipitate. If this thrombosin is dissolved in 

 dilute alkaline solution it clots readily when brought into contact with cal- 

 cium salts. Thrombosin may also be formed from fibrinogen by the action of 

 dilute acetic acid or nucleic acid (nuclein). Normal coagulation, according to 

 Lilienfeld, takes place as follows : After blood is shed there occurs a disinte- 

 gration of leucocytes (and blood-plates) resulting in the giving off of nuclein 

 compounds to the plasma. These nuclein substances, being dissolved in the 

 alkaline plasma, come in contact with the fibrinogen and decompose it, with 

 the formation of thrombosin. This latter substance then unites with the cal- 

 cium salts of the plasma to form fibrin, which, on this theory, might be defined 

 as a calcium compound of thrombosin. Lilienfeld's theory does not give a 

 satisfactory explanation of the nature of fibrin ferment, but is very valuable 

 in demonstrating that the essential act of clotting that is, of the formation 

 of fibrin is the union of calcium salts with a portion of the fibrinogen mole- 

 cule, and that this portion of the fibrinogen molecule may first be split off by 

 the action of acetic acid or the acid nuclein compounds. Until further inves- 

 tigations are made it is not possible to decide between the theories of Pekel- 

 haring and Lilienfeld. It is well, however, to emphasize the fact that there 

 is much in common between the two theories. Each holds that the fibrin is a 

 compound of calcium salts with a portion of the fibrinogen molecule, the latter 

 undergoing splitting during the act of clotting. According to Lilienfeld, this 

 splitting of the fibrinogen molecule is caused by nucleo-proteid, and the 

 thrombosin thus formed then combines with the calcium. According to Pekel- 

 1 Du Bois-Reymond's Archivfiir Physioloyif, 1893, p. 560. 



