36 THE BLOOD 



Composition of Blood. 



The blood is composed of a fluid part, the plasma, in which 

 float a great mass of small bodies, the blood corpuscles. The 

 plasma may be denned as the blood minus the corpuscles. These 

 are of three varieties: (i) The red corpuscles, or erythrocytes, 

 (2) the white corpuscles, or leucocytes and (3) the blood platelets, 

 or thrombocytes. The plasma is a thin slightly yellowish fluid 

 with a specific gravity of 1.026 to 1.029. Hence, the bright red 

 color of the blood is due to the red corpuscles which are held in 

 suspension in the plasma. The proportion of plasma to cor- 

 puscles is about two to one (Ho well). 



Plasma. 



Chemically, plasma is composed of water and about 10 per 

 cent, of solids, together with oxygen, carbon dioxide and nitrogen. 

 A thousand parts of plasma contain: (Halliburton.) 



Water 902 . 90 



Solids 97 . 10 



Proteins: i. Yield of fibrin 4.05 



2. Other proteins 78 .84 



Extractives (including fat) 5-66 



Inorganic salts 8.55 



The most important solids are the proteins, the chief of which 

 are: (i) Fibrinogen, (2) serum globulin, and (3) serum albumin. 

 Fibrinogen belongs to the globulin class of proteins, but differs 

 from serum globulin and may be separated from it. Fibrinogen 

 is the least abundant of the proteins. Serum globulin and serum 

 albumin form the chief proteins of the plasma. They may be 

 separated by the use of neutral salts. 



The extractives are substances other than proteins which 

 may be extracted from the dried residue by the use of water, 

 alcohol, or ether. The principal extractives are fats, sugar, 

 lecithin, cholesterin, lactic acid and urea. 



