COAGULATION 23 



experiments upon executed criminals. From these, the 

 weight of the blood had been found to be one-thirteenth 

 of the body weight. Haldane, however, puts the figure 

 at one-twenty fifth. 



When the volume of the blood is disturbed, the body 

 reacts so as to restore it to its normal value. When fluid 

 enters the body from the intestine, it does not materially 

 increase the blood- volume, for the excess is immediately 

 excreted by the kidney. When blood is lost by haemorrhage, 

 the volume is recovered by the passage of fluid from the 

 lymph spaces into the circulation, the normal number of 

 red corpuscles being restored later by increased activity 

 of the bone-marrow. 



At high altitudes the volume of the blood is diminished, 

 with the result that there is a relative concentration of 

 red blood corpuscles. This effect comes on within twenty- 

 four hours. After a few weeks the number of red corpuscles 

 is increased absolutely by heightened activity of the bone- 

 marrow. 



THE COAGULATION OF BLOOD 



The clotting of blood consists in the deposition in it 

 of a mesh work, consisting of a protein known as fibrin. 

 In this meshwork the corpuscles are entangled and from 

 it exudes a fluid — the serum. Clotting is essentially the 

 formation of fibrin. 



The conditions which determine the occurrence or non- 

 occurrence of fibrin-formation are very diverse. 



The process is hastened in drawn blood — 



1. By mechanical distvirbance ; 



2. By keeping it at body temperature ; 



3. By addition of serum or clot ; 



4. By addition of extracts of nuclear tissue ; 



and in vivo — 



5. By injury to the endothelial lining of the blood-vessel. 



