BLOOD. 



colored liquid the serum which gradually increases in quantity as the 

 clot diminishes in size, by contraction, until the separation is completed, 

 which occupies from twelve to twenty-four hours. 



The changes in the blood are as follows: 



Before coagulation. 



Liq. Sanguinis, 

 or 



consisting of 



Living blood. 



Plasma, 



Corpuscles, red and white. 

 After coagulation. 



Crassamentum. 1 



> containing 



Dead blood. 



Clot or coagulum, 

 Serum, 



containing 



Water 

 Albumin. 

 Fibrinogen. 

 Salts. 



Fibrin. 



Corpuscles. 



Water. 



Albumin. 



Salts. 



The serum, therefore, differs from the liquor sanguinis in not containing 

 fibrin. 



In from twelve to twenty-four hours the upper surface of the clot presents 

 a grayish appearance the buffy coat owing to the rapid sinking of the red 

 corpuscles beneath the surface, permitting the fibrin to coagulate without 

 them; this substance then assumes a grayish-yellow tint. Inasmuch as the 

 white corpuscles possess a lighter specific gravity than the red, they do not 

 sink so rapidly, and, becoming entangled in the fibrin, assist in forming the 

 buffy coat. Continued contraction gives a cupped appearance to the surface 

 of the clot. 



Inflammatory states of the blood produce a marked increase in the buffed 

 and cupped condition, on account of the aggregation of the corpuscles and 

 their tendency to rapid sinking. 



The Cause of Coagulation. Coagulation is due to the appearance of 

 fibrin, a derivative of an antecedent substance fibrinogen; the cause of the 

 conversion of the soluble fibrinogen into the insoluble fibrin is the presence 

 and activity of an agent termed thrombin. This agent is believed to be 

 a derivative of an antecedent substance prothrombin or thrombogen a sub- 

 stance always present in the blood and is a product of the decomposition of 

 leucocytes and the blood platelets. With thrombogen there is associated a 

 calcium salt which is essential for coagulation. If it is removed by the 

 addition of potassium oxalate coagulation does not take place. These 

 three substances prothrombin or thrombogen, a calcium salt and fibrinogen 



