THE BLOOD 109 



Pure plasma may be obtained from horse's veins by what is known 

 as the ' living test-tube ' experiment. If the jugular vein is ligatured 

 in two places, so as to include a quantity of blood within it, then 

 removed from the animal and hung in a cool place, the blood will not 

 coagulate for many hours. The corpuscles settle, and the supernatant 

 plasma can be removed with a pipette. 



The plasma is alkaline, yellowish in tint, and its specific gravity 

 is about 1,026 to 1,029. 



Its chief constituents may be enumerated as follows : 



1,000 parts of plasma contain 



Water 902-90 



Solids 97-10 



Proteins : 1, yield of fibrin . . 4*05 



2, other proteins . . 78'84 



Extractives (including fat) . . . 5'66 



Inorganic salts ...... 8'55 



In round numbers plasma contains 10 per cent, of solids, of which 

 8 per cent, are protein in nature. 



Serum contains the same three classes of constituents proteins, 

 extractives, and salts. The extractives and salts are the same in the 

 two liquids. The proteins differ, as is shown in the following 

 table : 



Proteins of PlcLsma Proteins of Serum 



Fibrinogen Serum globulin 



Serum globulin Serum albumin 



Serum albumin Fibrin ferment (nucleo- protein) 



The gases of the plasma and serum are small quantities of 

 oxygen, nitrogen, and carbonic acid. . The greater part of the oxygen 

 of the blood is combined in the red corpuscles with haemoglobin ; 

 the carbonic acid is chiefly combined as carbonates (see BESPIKATION). 



We may now consider one by one the various constituents of the 

 plasma and serum. 



A. Proteins, Fibrinogen. This is the parent substance of fibrin, 

 It is a globulin. It differs from serum globulin, and may be sepa- 

 rated from it by the fact that half saturation with sodium chloride 

 precipitates it. It coagulates by heat at the low temperature of 

 56 C. As judged from the yield of fibrin, it is the least abundant of 

 the proteins of the plasma (see table on upper part of this page). 



Serum globulin and serum albumin. These substances are con- 

 sidered in the practical exercises at the head of this lesson ; see also 



