THE BLOOD. 541 



of Delezenne l should be mentioned in this connection. He showed that 

 the blood of birds, reptiles, Batrachia, and fish coagulated but very slowly 

 of itself. If for example the blood of a bird be carefully removed so that 

 it does not come in contact at all with the tissues, it can be kept in vessels, 

 out of contact with dust, for a long time, without forming a clot. By 

 centrifugalizing such blood, plasma can be obtained which keeps until it 

 putrefies without the formation of any clot. If, however, a little blood, or 

 a little juice from the tissues, be added to such cell-free plasma, there is at 

 once a formation of fibrin. If the blood clots of itself, then we notice that 

 the clot is formed first at a place where there is present a considerable 

 amount of leucocytes. This experiment cannot be carried out with 

 the blood of mammals, for it coagulates too quickly. Evidently their 

 leucocytes are less resistant than those of the above-mentioned classes 

 of animals. The objection may be raised that in every case there is 

 the possibility that active fibrin-ferment may be carried to the blood of 

 plasma by the juices from the tissues, while the zymogen of this fibrin- 

 ferment which is contained in the blood itself, for some reason is not 

 changed into the active form. Morawitz 2 has proved, however, that this 

 objection is not well founded. He showed that the juice from the tissues, 

 even in the presence of calcium salts, was incapable of causing a fibrinogen 

 solution to coagulate. If, however, the extract from the tissues be 

 added to the blood itself, there is a marked acceleration of the coagulation 

 provided that the lime-salts are present. In the absence of lime-salts, the 

 extracts from the tissues are without action. 



Alexander Schmidt distinguished between accelerating and retarding 

 substances for the coagulating of the blood. He believed that these are 

 present in the leucocytes, and in all other cells of the bodies. The former 

 class of substances may be extracted with alcohol, while the latter cannot. 

 We can imagine that the substances which accelerate the clotting of blood 

 serve to activate the zymogen of the fibrin-ferment. Under normal condi- 

 tions, i.e., while the blood is circulating through the blood-vessels, there is 

 an equilibrium between these substances that accelerate and those that 

 retard its coagulation, whereas when clotting takes place, this equilibrium 

 is disturbed in favor of the former. Plausible though this hypothesis 

 may be, it must be emphasized that it is not based upon a careful analysis 

 of the separate processes. 



If we draw a picture of blood-coagulation in accordance with what has 

 been stated above, we may assume it to be well established that the blood, 

 or, better, the plasma, contains a substance, fibrinogen, which is an ante- 

 cedent of fibrin. This transformation of fibrinogen into fibrin is to be 



1 Compt. rend. soc. biol. 48, 782; Compt. rend. 122, 1281 (1896) ; Arch. Physiol. 1897, 

 333; Compt. rend. soc. biol. 49, 462, 489, and 507 (1897). 



a Arch. klin. Med. 79, 1 (1904); Hofmeister's Beitr. 4, 381 (1903); 6, 133 (1904). 



