170 THE BLOOD 



makes its appearance in the urine (glycosuria), when present in the blood in larger 

 amounts than 0.3 per cent.* Sugar is not a constituent of the corpuscles. 



The urea content of the blood varies between 0.02 and 0.15 per cent. It 

 increases after the ingestion of meat and decreases during starvation. ^ In normal 

 human blood, von Jaksch,^ found this body in amounts of 0.05 to 0.06 per cent. 

 An augmented protein metabolism or a retarded elimination of urea leads to an 

 accumulation of these substances in the blood. Traces of ammonia are also present. 

 The quantity of lactic acid varies considerably; as much as 0.071 per cent, has 

 been found. 



The Constituents of the Blood Plasma. — The liquid which serves 

 as the medium for the corpuscles, may be obtained by rapid centrifu- 

 galization, or by rendering the blood non-coagulable and permitting 

 the formed elements to settle. The supernatant portion of the blood 

 may be made to clot at any time by the addition of an agent possessing 

 the power of inciting coagulation. The clotting of the blood may be 

 said to be chiefly dependent upon the plasma, because the latter con- 

 tains all the substances essential for this process. 



The plasma is yellowish in color, alkaline in reaction, and possesses 

 a specific gravity of about 1.026 to 1.029. Its composition per 1000 

 parts is as follows: 



Water 902.90 



Solids 97. 10 



Proteins : 



Fibrin 4. 05 



Other proteins 78 . 84 



Extractives (including fat) 5 . 66 



Inorganic salts 8. 55 



Sodium chlorid is most abundant in human blood plasma. It forms 60 to 90 

 per cent, of the total mineral matter. Schmidt gives the following table for each 

 1000 parts of plasma : 



Mineral matter 8 . 550 



Chlorin 3.640 



SO, 0. 115 



PjOs . 191 



Potassium 0. 323 



Sodium 3.341 



Calcium phosphate . 311 



Magnesium phosphate . 222 



In general, it may be said that plasma contains 10 per cent, of 

 solids of which 8 per cent, are in the form of proteins. The latter are 

 classified as fibrinogen, serum-globulin, paraglobulin and serum- 

 albumin. Albumoses or peptones are not present. Inasmuch as the 

 plasma of coagulating blood separates into fibrin and serum, the pro- 

 teins contained therein, may be divided into those apportioned to the 

 fibrin and those contained in the serum. Among the former we have 

 fibrinogen, thrombogen, and kinase. The serum embraces proteins, 



^ E. L. Scott, Am. Jour, of Physiol., xxxiv, 1914, 271. (Literature.) 

 « Sch6ndorff, Pfluger's Archiv, liv, 1893, and Ixiii, 1896, 192. 

 » Festschrift fur v. Leyden, i, 1901. 



