1 64 THE BLOOD. 



diluting with water and neutralising it with dilute acetic acid (in excess 

 of which it easily dissolves). Like other globulins, it requires the 

 presence of a certain amount of salts, or weak alkali, to be dissolved in 

 water ; it is therefore precipitated by dialysis or by sufficient dilution 

 of its solutions in salts or in serum, even without the addition of an 

 acid. 



Fibrinogen. This is the substance to which the plasma of the blood 

 especially owes its property of so-called spontaneous coagulability ; which 

 led to the term " coagulable lymph " being applied to it by older writers. 1 

 It is precipitated from plasma along with serum globulin, by saturation 

 with magnesium sulphate or sodium chloride; the precipitation of 

 mixed globulins so obtained (the plasmine of Denis) forms a coagulable 

 liquid, on dissolving it in a more dilute Solution of salt. Fibrinogen is 

 entirely precipitated from plasma, or any other fluid containing it, by 

 half-saturation with sodium chloride ; 2 it can be re-dissolved in water 

 with the aid of the salt adhering to it, reprecipitated by half-saturation, 

 and so on until it is obtained in a condition which may be regarded as 

 approaching purity. But in contact with the salt solution it gradually 

 loses its solubility, and every time that it is precipitated less of the 

 precipitate redissolves on adding water ; the material which forms and 

 which remains undissolved in the dilute solution of salt resembles 

 fibrin in many physical and chemical characters, but is not similarly 

 rapidly swollen by dilute acids ; it may be termed par a- fibrinogen or 

 pseudo-fibrin. Fibrinogen dissolves also in dilute alkali, even in the 

 absence of neutral salts ; its alkaline solutions are clear, but its solutions 

 in neutral salt solutions are opalescent. It is precipitated from the 

 solution in weak alkali by careful neutralisation with acetic acid, and from 

 solutions in neutral salt solutions by slightly acidulating with the same 

 acid, but it is readily soluble in excess of the acid. The temperature of 

 heat coagulation of fibrinogen in salt solution is between 52 and 55 ; 3 

 but the whole of the dissolved proteid is not thrown down at this 

 temperature ; a small amount remains in solution, and is not coagulated 

 until the temperature of 65 C. is attained. According to Haminarsten, 4 

 this is due to the splitting of the fibrinogen, under the influence of 

 heat, into coagulated fibrinogen and a globulin, which is coagulated at 

 the higher temperature. If fibrinogen which has been obtained from 

 blood plasma by the above method of half-saturation with NaCl, and 

 purified by repeated re-solution and re-precipitation with acetic acid, be 

 dissolved in water rendered faintly alkaline by NaHO, . it gives a 

 coagulum-like precipitate (if sufficiently concentrated) a short time after 

 the addition of a lime salt. The coagulum resembles fibrin in many 

 respects, but, according to Hammarsten, it is not true fibrin, but a 

 combination of fibrinogen with lime. 5 



1 Houlston, Diss. Med. Inaug., " de Inflammatione," pp. 11, 12, 14, Lugd. But., 17C7. 

 See Hewson's Works, Introduction, p. xxxvii, edited by G. Gulliver, London, printed for 

 the Sydenham Society, 1846. 



2 Hammarsten, Arch. f. d. ges. Physiol., Bonn, 1879, Bd. xix. S. 563. 



3 Hammarsten, ibid., 1880, Bd. xxii. S. 431. 



4 Ibid., 1879, Bd. xix. S. 563. 



5 Hammarsten. Ztschr.f. physiol. Chem., Strassburg, 1896, Bd. xxii. S. 333. It is 

 unnecessary to add any ferment or nucleo-proteid to the solution to produce the result, but 

 there is no doubt that nucleo-proteid may be present along with the fibrinogen. It was 

 shown by Lilienfeld (Ztschr. f. physiol. Chem., Strassburg, 1895, Bd. xx. S. 89) that 

 fibrinogen prepared by Hammarsten's method contains nuclein ; from this he inferred that 

 it is a nucleo-proteid, and not a globulin. But the amount of nuclein present is not sufficient 



