CHEMICAL EXAMINATION OF THE BLOOD. 329 



The Plasma. 



In order to obtain blood-plasma it is necessary to prevent coagu- 

 lation of the blood. This may be accomplished in various ways. 

 It has thus been found that following the intravenous injection of 

 certain albumoses (peptones), or of an infusion of the mouth parts 

 of the officinal leech (hirudin), as also after ligation of the bloodvessels 

 of the liver and intestines, the blood remains liquid after being 

 shed. On allowing it to stand at a low temperature the blood- 

 corpuscles settle to the bottom, when the supernatant fluid may 

 be siphoned oif ; or the blood may be centrifugalized at once and 

 separation of the cellular elements effected in this way. Blood- 

 plasma that has been obtained after the injection of albumoses is 

 termed albumose-plasma, or, less correctly, peptone-plasma, in con- 

 tradistinction to salt-plasma, which results when blood is received in 

 a solution of a neutral salt, whereby coagulation is also prevented. 

 To this end it is best to employ a saturated solution of sodium 

 sulphate or a 10 per cent, solution of sodium chloride, to which the 

 blood is added in an equal amount. A saturated solution of magne- 

 sium sulphate may likewise be used, in the proportion of one part 

 for three parts of blood, but is not so satisfactory, as it causes pre- 

 cipitation of certain albumins which are essential to coagulation. 

 After standing for twenty-four hours the plasma may be siphoned 

 off, or may be separated from the corpuscles at once by centrifugation. 



As coagulation of the blood is dependent upon the presence of 

 soluble calcium salts, coagulation may also be prevented by the 

 addition of ammonium oxalate (0.1 per cent.) or sodium citrate 

 (1.0 per cent.). Plasma obtained in this manner is spoken of as 

 oxalate or citrate plasma. 



Of especial value in these examinations is the blood of the horse, 

 in which coagulation occurs much more slowly than in that of 

 mammals. If this is available, it is only necessary to receive it in 

 a narrow cylinder surrounded with a freezing-mixture. Kept in 

 this manner it will remain liquid for several days. 



Separated from the corpuscles, the plasma is a clear, straw-colored, 

 slightly viscid fluid, of alkaline reaction, and a specific gravity 

 varying between 1.026 and 1.029 in man. It is capable of under- 

 going coagulation, like the native blood, and is thus converted into 

 blood-serum. Its general chemical composition has already been 

 considered. It contains but 8.2 per cent, of solids, of which 6.9 

 per cent, is represented by albumins. These are serum-albumin, 

 serum-globulin, and fibrinogen. The relation between these bodies 

 is subject to considerable variations. In all animals, however, the 

 globulins predominate, and in some indeed, as in snakes, serum- 

 albumin is apparently absent. In the horse the globulins con- 

 stitute about 64.6 per cent, of the total amount of albumins. In 

 1000 parts by weight Hammarsten thus found 38.4 parts of serum- 

 globulin, 6.5 parts of fibrinogen, and 24.6 parts of serum-albumin. 



