448 BLOOD AND LYMPH. 



C117H182N30SO38 + h^iO. Paraglobulin occurs in blood, in lymph, 

 and in the normal and pathological exudations. The amount of 

 paraglobulin present in blood varies in different animals. Among 

 the mammalia the amount ranges from 1.78 per cent, in rabbits to 

 4.56 per cent, in the horse. In human blood it is given as 3.10 

 per cent., being less in amount, therefore, than the serum-albumin. 

 Paraglobulin as obtained from blood-serum by half-saturation 

 with ammonium sulphate or full saturation with magnesium sul- 

 phate does not behave like a chemical individual. Portions of it, 

 for instance, are precipitated by CO2 or by dialysis, and portions 

 are not so precipitated. Recently, therefore, it has been assumed 

 that paraglobulin is, in reality, a mixture of two or possibly three 

 different, although related, proteins. The separation usually 

 given is into euglobuhn and pseudoglobulin, euglobulin being the 

 portion precipitated by ammonium sulphate when added to one- 

 third saturation (28 to 33 per cent.), and pseudoglobulin the por- 

 tion precipitated only by one-half saturation (34 to 50 per cent.). 

 The latter portion shows properties more nearly related to the 

 albumins.* The whole basis of classification is, however, un- 

 satisfactory and provisional (see Appendix). 



Fibrinogen is a protein belonging to the globulin class and ex- 

 hibiting all the general reactions of this group. It is distinguished 

 from paraglobulin by a number of special reactions; for example, 

 its temperature of heat coagulation is much lower (56° C), and 

 it is completely thrown down from its solutions by saturation 

 with sodium chlorid as well as with magnesimri sulphate. Its most 

 important and distinctive reaction is, however, that under proper 

 conditions it gives rise to an insoluble protein, fibrin, whose forma- 

 tion is the essential phenomenon in the coagulation of blood. 

 Fibrinogen has a percentage composition, according to Hammar- 

 sten, of: C, 52.93; H, 6.90; N, 16.66; S, 1.25; 0,22.26; while its 

 molecular composition, according to Schmiedeberg, is indicated by 

 the formula CiogHig^NjoSOg^. 



Fibrinogen is found in blood-plasma, lymph, and in some cases, 

 though not always, in the normal and pathological exudations. It 

 is absent from blood-serum, being used up during the process of 

 clotting. It occurs in very small quantities in blood, compared 

 with the other proteins. Estimates of the amount of fibrin, which 

 cannot differ very much from the fibrinogen, show that in human 

 blood it varies from 0.22 to 0.4 per cent. ; in horse's blood it may 

 be more abundant, — 0.65 per cent. There is some evidence to 

 indicate that the fibrinogen is produced in the liver, or at any rate 

 that this organ is concerned in some way in its production. Thus 



* Forges and Spiro, "Beitrage zur chem. Physiol, u. Pathol.," .3, 277, 

 1903; and Freund and Joachim, "Zeitschrift f. physiologische Chemie," 36, 

 407, 1902. 



