CHAP. II.] THE BLOOD. 41 



vessels with one-third of its volume of a saturated solution of mag- 

 nesium sulphate. The mixture is then subjected to nitration in 

 order to obtain salted plasma free from corpuscles. As filtration is, 

 however, often very difficult from clogging of the filter, and at all 

 times very slow, I have, in repeating Hammarsten's experiments, 

 subjected the mixture of blood and magnesium sulphate to the 

 action of the centrifugal machine (see p. 58); in this way, in about 

 half an hour, perfectly clear salted plasma may be obtained in con- 

 siderable quantities. 



To the salted plasma there is now added an equal volume of a 

 saturated solution of common salt; the fluid instantly becomes turbid, 

 and in two or three minutes an abundant flaky precipitate forms. 



From this point the process may be conveniently modified as follows : 

 The liquid with the suspended precipitate is carefully stirred, whereby 

 the precipitate usually floats to the surface and forms a thick dense layer 

 on the top of the liquid, which is then syphoned off. The precipitate is 

 now well mixed with a solution made by diluting saturated solution of 

 common salt with an equal volume of water, the quantity of the half 

 saturated solution of salt being equal to that of MgSO 4 plasma which was 

 employed in the process. The precipitate floats up to the surface, the 

 NaCl solution is syphoned oft', and a fresh quantity of the same added; the 

 process of washing and syphoning being repeated not less often than six 

 times. The fibrinogen is then collected on a separate funnel, pressed 

 between folds of filtering paper, suspended in water and the solution 

 filtered. The whole process can be completed in from 2J 3 hours 1 . 



This is separated by filtration, and may be washed with saturated 

 solutions of Nad. The precipitate is freed from much adhering 

 moisture by pressing between folds of blotting paper, and is then 

 mixed with a solution of common salt containing 6 8 p.c. of the 

 salt, and in this it soon dissolves. The solution is filtered, and to it 

 is added an equal volume of saturated solution of NaCl, which again 

 throws down fibrinogen, but in a purer condition than at first, in 

 the form of gelatinous flakes. The precipitate may be again 

 dissolved in the weak solution of sodium chloride and precipitated a 

 third time. It may then be assumed to be pure ; it is at least free 

 from the minutest traces of paraglobulin and of serum-albumin. In 

 consequence of the common salt which adheres to it, the precipitate 

 is found to be soluble in pure water. A solution of fibrinogen thus 

 obtained is found not to be spontaneously coagulable, but to yield 

 fibrin when mixed with serum or other solutions possessing the 

 peculiar ferment action to be subsequently referred to when speaking 

 of Theories of coagulation. 



Solutions of fibrinogen containing 1 5 p.c. of NaCl coagulate at 

 52 C. 55C. (Hammarsten, Frederique). 



Solutions of fibrinogen coagulate at 56 C. according to Frederique, 



1 Hammarsten, "Ueber das Fibrinogen." Pfliiger's Archiv, Vol. xix. (1879) p. 563, 

 et seq. 



