BLOOD AND H^MOPOIETIC ORGANS 97 



different individuals, but in the same individual at 

 different times, and this must be borne in mind when 

 attempts are made to estimate the coagulation time 

 clinically. 



To the question, Why does the blood not clot inside 

 the living vessels ? it may be replied that such an occur- 

 rence is apparently prevented (1) by the active move- 

 ment of the blood, (2) by the absence of free fibrin 

 ferment, (3) by an influence not understood exerted 

 by the lining of the living and healthy vessel. It has 

 recently been suggested that the absence of clotting in 

 the living body is due to the constant neutralization of 

 fibrin ferment (plasmase), produced by leucocyte dis- 

 integration by an antibody or thrombase.* 



If these conditions are not fulfilled, clotting can and 

 does occur. If the blood stagnates for a time, as it may 

 do in the interior of a dilated heart, for example, clotting 

 may occur; or if anything injures the leucocytes and 

 causes them to break down, fibrin ferment is liberated, 

 and clotting ensues. This has been taken advantage of 

 in the treatment of aneurysrn. By the introduction of a 

 coil of wire into the sac, separation out of leucocytes and 

 platelets is brought about and clotting is promoted. If, 

 again, the wall of a vessel becomes diseased, it may lose 

 its power of preventing clotting, and actually promote 

 the process just as a foreign body does. Hence clotting 

 is not infrequent in atheromatous vessels. The fact that 

 the presence of calcium salts favours the coagulation 

 of blood has been turned to therapeutic account. In 

 .patients who are the subject of jaundice the blood tends 

 * Buckmaster, loc. cit., p. 217. 



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