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 para-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 Hammarsten, 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 Inflamniaticme," pp. 11, 12, 14, Lugd. Bat., 1767. 
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 
