358 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



work. It was shown in microscopic preparations of coagulated blood that the 

 fibrin threads often radiated from broken-down leucocytes an appearance 

 which seemed to indicate that the leucocytes served as points of origin for the 

 deposition of the fibrin. When the blood-plates were discovered a great deal 

 of microscopic work was done tending to show that these bodies also are con- 

 nected with coagulation in the same way as the leucocytes, and serve probably 

 as sources of fibrin ferment. In microscopic preparations the fibrin threads 

 were found to radiate from masses of partially disintegrated plates ; and, more- 

 over, it was discovered that conditions which retard or prevent coagulation of 

 blood often serve to preserve the delicate plates from disintegration. At the 

 present time it is generally believed that there is derived from the disintegra- 

 tion of the leucocytes and blood-plates something which is necessary to the 

 coagulation of blood, but there is some difference of opinion as to the nature 

 of this substance and whether it is identical with Schmidt's fibrin ferment. 

 Pekelharing thinks that the substance set free from the corpuscles and plates 

 is a nucleo-proteid, but that this nucleo-proleid is not capable of acting upon 

 fibrinogen until it has combined with the calcium salts of the blood. According 

 to his view, therefore, fibrin ferment, in Schmidt's sense, is a compound of cal- 

 cium and nucleo-proteid. Lilienfeld has shown by chemical reactions that 

 blood-plates and nuclei of leucocytes contain nucleo-proteid material which in 

 all probability is liberated in the blood-plasma by the disintegration of these 

 elements after the blood is shed. As he has shown also that this nucleo- 

 proteid material with the aid of calcium salts acts upon the fibrinogen to pro- 

 duce fibrin, it would seem clear that the so-called fibrin ferment is really a 

 nucleo-proteid compound. Lilienfeld contends, however, that solutions of 

 fibrin ferment prepared by Schmidt's method do not contain any nucleo-proteid 

 material, and that, although the liberation of the nucleo-proteid material is what 

 starts normal coagulation of blood, nevertheless so-called fibrin ferment is some- 

 thing entirely different from uucleo-proteid. In this point, however, his results 

 are contradicted by the experiments of Pekelharing and of Halliburton, who 

 both find that solutions of fibrin ferment prepared by Schmidt's method give 

 distinct evidence of containing nucleo-proteid material. "We may conclude, 

 therefore, that the essential element of Schmidt's fibrin ferment is a nucleo- 

 proteid compound. Whether or not this nucleo-proteid can act upon fibrinogen 

 directly, as Lilienfeld claims, or must first combine with calcium salts, as held 

 by Pekelharing, is a matter which must be left to future investigation. 



Intravascular Clotting. Clotting may be induced within the blood- 

 vessels by the introduction of foreign particles, either solid or gaseous for 

 example, air or by injuring the inner coat of the blood-vessels, as in ligat- 

 ing. In the latter case the area injured by the ligature acts as a foreign 

 surface and probably causes the disintegration of a number of corpuscles. 

 The clot in this case is confined at first to the injured area, and is known 

 as a " thrombus." Intravascular clotting more or less general in occurrence 

 may be produced by injecting into the circulation such substances as leucocytes 

 obtained by macerating lymph-glands, extracts of fibrin ferment, solutions of 



