CLOTTING OF BLOOD 235 



This process whereby the fluid content of the gel is decreased 

 is common to gels and is called syneresis. 



Historical. 



Observers at first thought that living tissue had a restraining 

 influence. They noticed that in the living tissue the blood did 

 not clot. Lister formed a living test-tube by ligature of the 

 aorta and showed that the blood did not clot until a foreign body 

 such as glass was introduced. 



This demonstrated that clotting was not due to (1) removal 

 from living vessels, (2) stoppage of the circulation, (3) cooling or 

 (4) to contact with air. This latter fact has been confirmed by 

 the observation that blood clots as readily in a vacuum as in air. 

 Further, air embolism and caisson disease do not lead to intra- 

 vascular clotting. Nor is clot formation due to cooling. As a 

 matter of fact reduction of temperature lengthens the time taken 

 to produce a clot and, if the plasma is cooled sufficiently, may 

 prevent it altogether. 



The classical work on blood clotting was performed by Andrew 

 Buchanan, Professor of Physiology at Glasgow, who gave ex- 

 planations of the process to the Glasgow Philosophical Society, 

 in March, 1844, and February, 1845. Using hydrocele fluid from 

 the tunica vaginalis of a horse he showed that it would clot if to it 

 were added a drop or two of blood, of clot washings, of serum or of 

 tissue juice. He compared the process to the curdling of milk 

 by rennin and considered that the white corpuscles or leucocytes 

 were the active agent. 



In 1861, Schmidt, who had devoted some thirty years to the 

 work, proved that : 



(i) Fibrinogen, the precursor of the clot, was a globulin in the 

 plasma. 



(ii) There was a fibrin-former in plasma, in serum and in clot 

 washings. 



He also showed that this fibrin-former (now called thrombin) 

 did not exist as such in the blood but only appeared after treatment 

 with a fibrin-ferment or -kinase. That is, the clotting scheme as 

 he left it appears as follows (modern names) : 



Fibrinogen + Thrombin = Fibrin (or Clot) 

 Pro-thrombin + " Thrombokinase." 



Arthus and Pages in 1890 showed the need of calcium in the 

 clotting process. 



