326 THE BLOOD. 



lation takes place after ligation of an artery, and that the coagulum 

 invariably extends as far as the next collateral vessel. That the 

 nutrition of the intima is here seriously interfered with cannot be 

 doubted. Similarly we find a more or less extensive thrombosis 

 in atheromatous vessels, not to speak of the process of clotting in 

 association with wounds. In such cases it appears that owing to the 

 lesion of the endothelial coat an aggregation of leucocytes occurs 

 in the aifected parts, which in turn results in the death and disso- 

 lution of many of the cells at these places. Contact with a foreign 

 substance, and as such diseased or dying endothelial cells must be 

 viewed, in some manner brings about the early dissolution of the 

 leucocytes, and we find accordingly that on introducing a silk thread 

 into the bloodvessel of a living animal coagulation takes place 

 around the foreign body. Similarly, it may be observed that when 

 blood is received in a vessel, the walls of which have been carefully 

 lubricated with vaselin, coagulation is greatly delayed, but may be 

 brought about at once on introducing bits of foreign material, such 

 as dust or ashes and the like. 



While we have thus seen that coagulation will occur within the 

 living body whenever foreign material is present, we have not as yet 

 offered an explanation for the non-occurrence of coagulation when 

 such influences are not at work. That leucocytes are constantly 

 broken down in the living organism cannot be questioned. It is 

 possible, however, that the amount of nucleohiston, or fibrin ferment, 

 as the case may be, which is thus formed, is too small at any one 

 time to exert its special activity. On the other hand, it is conceiv- 

 able that such decomposition may take place within certain organs 

 of the body, such as the spleen and the liver, and that the nucle- 

 histon, which is here set free, is again utilized in the construction of 

 new cells. The nucleohiston, moreover, contains another radicle, 

 the albumose-like histon, which has exactly the opposite effect upon 

 coagulation. For whereas the injection of leuconuclein into the cir- 

 culation of living animals rapidly brings about the death of the 

 animal from thrombosis, histon injections render the blood refractory 

 to coagulation. Such plasma is termed histon-plasma, and it is to 

 be noted that this coagulation can later be brought about only through 

 the addition of the leuconuclein or nucleinic acid. It is thus possi- 

 ble that during the dissolution of the leucocytes in the living animal 

 the leuconuclein is in some manner prevented from exercising its 

 special activity, while the histon further prevents coagulation in 

 itself. The primary factor, however, upon which the occurrence or 

 non-occurrence of coagulation in the living body probably depends, 

 is the extent to which the leucocytes are undergoing decomposition. 



Rapidity of Coagulation. The rapidity with which coagu- 

 lation of the blood occurs after being shed varies with different 

 animals, with the districts from which the blood is taken, etc. 

 In birds it thus occurs after one and a half minutes ; in man 

 after from three to four minutes ; while in cold-blooded animals 



