CH. XXVI.] PROTEIDS OF THE BLOOD. 



of fibrin-ferment, or liquids like serum that contain fibrin-ferment, 

 they always yield fibrin. 



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 clot 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 1026 to 1029. 1000 parts of plasma contain : 



Water . . . . 



Solids 



Proteids : i, yield of fibrin 



2, other proteids . 

 Extractives (including fat) 

 Inorganic salts 



902-90 



97-10 



4'05 



78-84 



5-66 



8-55 



lu round numbers, plasma contains 10 per cent, of solids, of 

 which 8 are proteid in nature. Note, however, the comparatively 

 small yield of fibrin. 



Serum contains the same three classes of constituents pro- 

 teids, extractives, and salts. The extractives and salts are the 

 same in both liquids. The proteids are different, as is shown in 

 the following table : 



Proteid* of Plasma. Proteids of Serum. 

 Fibrinogen. Serum globulin. 



Serum globulin. Serum albumin. 



Serum albumin. Fibrin-ferment. 



The gases of 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. The gases 

 of the blood have already been considered under Respiration (see 



P- 377)- 



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

 plasma and serum. 



A. Proteids. Filtrinoyen. This is the substance acted on by 

 fibrin-ferment. It yields, under this action, an insoluble product 

 callcil jlhrin and a soluble proteid of the globulin class. 



Fibrinogen is a globulin. It differs from serum globulin, and 

 may be separated from it, by making use of the fact that half- 

 saturation with sodium chloride precipitates it. It coagulates by 

 heat at the low temperature of 56 C. 



Serum <ilt>idin and serum albumin. These substances exhibit 

 the usual differences already described between albumins and globu- 

 lins (p. 397). Both are coagulated by heat at a little over 70 C. 



