THE BLOOD. 233 



COMPOSITION OF PLASMA. 



Water 90 .00 



f Serum-albumin 4-5 



Proteins . . . \ Paraglobulin 3 .40 



[ Fibrinogen o . 30 



Fatty matters . 0.25 



Sugar o . 10 



Extractives o . 60 



Inorganic salts 0-85 



100.00 



Serum-albumin. Of the protein constituents of the blood, serum- 

 albumin is the most abundant, existing to the extent of from 4 to 5 per cent. 

 From its similarity to egg-albumin it is regarded as holding an important 

 position as a nutritive agent, for it is out of this common protein that in all 

 probability each individual tissue elaborates the special protein characteristic 

 of it, since during starvation the albumin steadily diminishes in amount. As 

 it passes through the walls of the capillary vessels it is found in the lymph, 

 pericardial fluid, and similar secretions in various parts of the body, as well 

 as in various pathologic transudates. It is also present in serum. While 

 circulating in the lymph-spaces the serum-albumin is utilized in replacing 

 the proteins which have undergone disintegration during tissue metabolism. 

 Its supply in the blood is maintained by the absorption of peptones or simpler 

 products of protein digestion, e.g., amino-acids, which are formed from the 

 proteins of the food and which during the time of absorption are changed in 

 some unknown way into serum-albumin. It is readily obtained from plasma 

 or serum by saturating either of these fluids with magnesium sulphate, when 

 all the proteins except serum-albumin are precipitated. After their removal 

 the remaining fluid is subjected to a temperature of from 70 to 75 C., when 

 the serum-albumin is precipitated in a coagulable form, after which it can 

 be removed and its chemic features determined. 



Paraglobulin. This protein, though present in plasma, is best obtained 

 from serum when this fluid is saturated with magnesium sulphate. As the 

 line of saturation is approached the fluid becomes turbid, and after a few 

 minutes a fine white precipitate occurs. It can then be collected on a filter, 

 dried, and its chemic properties determined. In its reactions it resembles 

 the various members of the globulin class. The amount varies from 2 to 4 

 per cent, in the blood of man. As to the physiologic importance or ante- 

 cedents of paraglobulin nothing is definitely known. Its constant presence 

 in the blood would indicate that it plays an equally important, though per- 

 haps different, part with serum-albumin in the nutrition of the body. 



Fibrinogen. This protein can be obtained from plasma, lymph, 

 pericardial, and peritoneal fluids, as well as from hydrocele fluid. It is, 

 however, not to be obtained from serum, as it is removed from the blood 

 during the formation of solid fibrin. It is normally present in the blood in 

 very small quantity, amounting to not more than 0.22 to 0.33 parts per 

 hundred. Fibrinogen may be obtained from plasma which has been pre- 

 vented from coagulating, by the addition of magnesium sulphate in certain 

 quantities or by the addition of a saturated solution of sodium chlorid. In 

 a few minutes a flaky precipitate occurs. By repeated washing and pre- 

 cipitation with sodium-chlorid solutions of varying strength, the fibrinogen 

 may be obtained in a pure state. The history of fibrinogen is unknown, 



