338 THE BLOOD. 



elements calcium is constantly present, and, as has been seen, its 

 formation is largely dependent upon the presence of a soluble 

 calcium salt. 



The amount of fibrin which may be obtained from the blood, 

 notwithstanding its bulk, does not exceed 0.10.4 per cent. 



Estimation. In order to determine the amount of fibrin in a 

 given volume of blood, from 30 to 40 c.c. are placed in a previously 

 weighed beaker, which is closed with an India-rubber cap. Through 

 the centre of this passes a piece of whalebone that is firmly fixed 

 and provided with a rudder-like end, which dips into the blood. 

 This is now defibrinated by beating with the whalebone paddle, 

 when the beaker is again weighed with its contents. The differ- 

 ence, as compared with the first weight, indicates the weight of the 

 blood. The beaker is then filled with water and the mixture again 

 beaten. The fibrin is allowed to settle, and after being washed by 

 decantation with normal salt solution it is collected on a filter of 

 known weight. On this it is further washed with normal salt solu- 

 tion until free from coloring-matter ; it is then extracted with boiling 

 alcohol, then with ether, and finally dried at 115 C. and weighed. 



The question, why the blood does not coagulate within the vessels 

 of the body where fibrinogenic material is available, and where leuco- 

 cytes no doubt undergo degeneration, has been variously answered. 

 On the one hand, it is stated that the integrity of the endothelial 

 lining is here of prime importance, and that coagulation will occur 

 whenever this is impaired. As a matter of fact, we find that coagu- 

 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 affected 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 the integrity of the bloodvessel walls is thus unquestion- 

 ably of moment in preventing coagulation in the living organism, we 

 may also imagine that an antiferment antithrombin may be present 

 in the blood which prevents the activation of the ferment. Pugliese 

 has shown, as a matter of fact, that such substances are formed in 

 the liver and muscle tissue. 



