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 defined as the blood minus the corpuscles. 

 These are of three varieties : ( I ) The red corpuscles, or ery- 

 throcytes, (2) the white corpuscles, or leukocytes, 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 corpuscles 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: (Hallibur- 

 ton.) 



Water , 902.90 



Solids 97-io 



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 separ- 

 ated from it. Fibrinogen is the least abundant of the pro- 

 terns. 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. 



