CHEMICAL EXAMINATION OF THE BLOOD. 313 



termed albumose-plasma, or, less correctly, peptone-pfafina, 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 gne 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 apparently dependent upon the 

 presence of soluble calcium salts, coagulation may also be prevented 

 by precipitating with ammonium oxalate those which are present in 

 the blood. To this end the blood is received in a solution of am- 

 monium oxalate, such that the quantity of the latter present in 

 the mixture amounts to about 0.1 per cent. This constitutes 

 oxalate-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. 

 Of these albumins, fibrinogen is of especial interest, as it represents 

 the mother-substance of fibrin, and is thus intimately connected with 

 the process of coagulation. 



Fibrinogen. Isolation. Fibrinogen is most convenientlv ob- 

 tained from the plasma by half-saturation with sodium chloride 

 i. e., by treating one volume of the plasma with an equal volume of 

 a saturated solution of common salt. The resulting precipitate of 

 fibrinogen is filtered off, washed with a half-saturated solution of 

 sodium chloride, and dissolved in an 8 per cent, solution of the salt. 

 To further purify the substance, this solution is re-precipitated, red is - 

 solved, and the process repeated twice. The final precipitate is 



