452 THE BLOOD [CH. XXIX. 



main those of Morawitz. Ho well regards the lack of coagulation seen in birds' 

 blood, and peptone blood, as due to excess of antithrombin, but holds that throra- 

 bokinase (or thromboplastin, as he terms it) brings about clotting, not by activating 

 thrombogen, but by neutralising antithrombin. According to him, also, thrombo- 

 plastin is probably a lipoid of the phosphatide group. 



The Plasma and Serum. 



The liquid in which the corpuscles float may be obtained by 

 employing one or other of the methods already described for pre- 

 venting the blood from coagulating. The corpuscles, being heavy, 

 sink, and the supernatant plasma can then be removed by a pipette 

 or siphon ; the separation can be more rapidly effected by the use of 

 a centrifugal machine. 



On counteracting the influence which has prevented the blood 

 from coagulating, the plasma then itself coagulates. Thus plasma 

 obtained by the use of cold clots on warming gently } plasma which 

 has been decalcified by the action of a soluble oxalate clots on the 

 addition of a calcium salt ; plasma obtained by the use of a strong 

 solution of neutral salt coagulates when this is diluted by the addition 

 of water, the addition of fibrin-ferment being necessary in most cases ; 

 where coagulation occurs without the addition of fibrin-ferment no 

 doubt some is present from the partial disintegration of the corpuscles 

 which has already occurred. Pericardial and hydrocele fluids 

 resemble pure plasma very closely in composition. As a rule, 

 however, they contain few or no white corpuscles, and do not clot 

 spontaneously, but after the addition of fibrin-ferment, or of liquids 

 such as 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 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 are protein in nature. Fibrinogen, as judged from the yield of 

 fibrin, is the least abundant of the proteins present. 



Serum contains the same three classes of constituents proteins, 

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



