COAGULATION. . 421 



artificial or unusual conditions, as stated in the next paragraph, 

 such substances may be produced. 



Intravascular Clotting. As is well known, clots may form 

 within the blood-vessels in consequence of the introduction of for- 

 eign material of any kind. Air, for instance, that has gotten into 

 the veins, if not absorbed, may act as a foreign substance and 

 cause the same chain of events as when the blood is shed, namely, 

 the disintegration of formed elements, formation of thrombin, and 

 clotting. So also when the internal coat of a blood-vessel is in- 

 jured as, for instance, by a ligature the altered endothelial cells 

 act as a foreign substance. If the circulatory conditions are favor- 

 able for instance, if the ligated artery causes a stasis of blood at 

 that point there may be an agglutination of the blood plates, 

 starting at the injured surface, and the subsequent formation of a 

 clot. Intravascular clotting may also be produced by the injection 

 of other substances. Calcium solutions added in quantity sufficient 

 to notably raise the calcium percentage of the plasma distinctly 

 favor the process of clotting and may lead to the formation of 

 intravascular clots. So, too, injections of thrombin or of leucocytes 

 as obtained from macerated lymph glands cause clotting. In 

 this latter case, however, it has been noticed that if the quantity 

 injected is not sufficient the coagulability of the blood may be 

 distinctly retarded instead of being accelerated. This fact has been 

 accounted for on the hypothesis that in the disintegration of the 

 foreign leucocytes two products are formed, one tending to acceler- 

 ate coagulation (positive phase of the injection) and one tending to 

 retard it (negative phase). Lilienfeld* has made this hypothesis 

 more specific by showing that lymphocytes (and blood plates) 

 yield a nucleoproteid which in turn on decomposition furnishes a 

 second nucleoproteid, leuconuclein, whose presence favors coagula- 

 tion, and a simple proteid, histon, whose action retards clotting. 

 Delezennej has still further added to the hypothesis by experiments 

 which indicate that the element favoring coagulation (leuconuclein) 

 is removed or destroyed by the liver. When an insufficient quan- 

 tity of leucocytes is injected into the circulation the histon action 

 may predominate, causing retarded coagulation, while with larger 

 quantities and a more extensive decomposition the leuconuclein 

 may bring about clotting before it is completely destroyed by the 

 liver. 



Means of Hastening or of Retarding Coagulation. Blood 

 coagulates normally within a few minutes, but the process may be 

 hastened by increasing the extent of foreign surface with which it 

 comes in contact. Thus, agitating the liquid when in quantity, or 

 the application of a sponge or a handkerchief to a wound, hastens 

 * Lilienfeld, "Zeitschrift f. physiol. Chemie," 18, 473. f Loc. tit. 



