CHEMICAL COMPOSITION OF BLOOD-PLASMA. 425 



it is completely thrown down from its solutions by saturation with 

 sodium chlorid as well as with magnesium 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; O, 22.26; while its 

 molecular composition, according to Schmiedeberg, is indicated by 

 the formula C 108 H 162 N 30 S0 34 . 



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. There is no good method of determining 

 quantitatively the amount of fibrinogen, but 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. As to the 

 origin and the special physiological value of this protein we are, if 

 possible, more in the dark than in the case of paraglobulin, with the 

 exception that fibrinogen is known to be the source of the fibrin of 

 clotted blood. But clotting is an occasional phenomenon only. 

 What nutritive function, if any, is possessed by fibrinogen under 

 normal conditions is unknown. No satisfactory account has been 

 given of its origin. It has been suggested by different investigators 

 that it may come from the nuclei of disintegrating leucocytes (and 

 blood plates) or from the dissolution of the extruded nuclei of newly 

 made red corpuscles, but here again we have only speculations, that 

 can not be accepted until some experimental proof is advanced to 

 support them. It may be added that there is some evidence to 

 indicate that the fibrinogen is produced in the liver. Thus Doyon 

 and his co-workers * have shown that when the fibrinogen is re- 

 moved from blood by defibrinating and the blood is then returned 

 to the animal, new fibrinogen is produced within a few hours. 

 In frogs, at least, the new fibrinogen is not manufactured if the 

 liver is removed, and in dogs it is also stated that after removal 

 of the liver the blood may become incoagulable owing to a disap- 

 pearance of fibrinogen. 



The following table t gives some recent results of analyses of 

 blood which indicate the average amounts of the different proteins 

 in the blood-plasma of several animal's. The figures give the weight 

 of the protein in grams for 100 c.c. of plasma. 



* Doyon et al., "C. R. Soc. de Biol.," lx., 606, 681, 860. See also Nolf. 

 "Archives internat. de Physiol.," 1905, iii., 1. 

 f Lewinski, he. cit. 



