138 THE BLOOD 



blood, liver, etc.; the lipolytic or fat-splitting ferments, and the proteolytic 

 ferments. From their property of producing not only hydrolytic cleavage 

 but the reverse reactions of synthesis these ferments hold one of the most 

 significant positions among the plasma constituents. 



Inorganic Substances. The total inorganic salts of human plasma 

 amount to from 0.80 to 0.89 per cent. By the recent titration method of 

 Cramer, the sodium ran 323 to 344 milligrams per 100 cubic centimeters 

 of serum. The chief salt is sodium chloride which constitutes over half 

 the total and contributes largely to the osmotic pressure of the blood. 

 Curiously enough only a minimal quantity of potassium salt is present in 

 the plasma, from 18 to 21 milligrams in a hundred grams. The potassium 

 exists as sulphate and basic phosphate. The calcium is very constant in 

 normal serum, from 9.3 to 9.9 milligrams in a hundred cubic centimeters 

 of serum. It is probably in the blood as a phosphate. The calcium con- 

 tent varies greatly in disease, is depressed in parathyroid tetany. 



The Serum. The serum is the liquid part of the blood or of the plasma 

 which remains after the fibrin has been formed and removed. It is a 

 transparent yellowish fluid with a specific gravity of 1025 to 1032. Serum 

 is ordinarily obtained free from blood corpuscles by whipping the blood, 

 that is removing the fibrin as fast as it forms and then sedimenting the 

 corpuscles in the centrifugal machine. It may be obtained by allowing 

 blood to clot in a test tube or beaker and then stand in the cold. The 

 clot contracts, squeezing out the clear yellowish straw-colored serum. In 

 quantitative chemical analysis the serum is essentially of the same compo- 

 sition as plasma, in fact serum is usually taken for such quantitative work. 

 It differs from plasma only in the loss of the fibrin or the fibrin factors 

 which go to form fibrin. It is usually rich in thrombokinase or fibrin 

 ferments. The percentages given above for the salts of plasma were 

 actually determined on serum. 



The Composition of the White Corpuscles. The white corpuscles 

 are comparatively undifferentiated cellular elements, hence possess the 

 chemical composition of protoplasm. Lillienfeld has made an analysis 

 of the leucocytes of thymus gland from the calf, which contain 11.49 P er 

 cent, of solids, as follows: 



In 100 Parts of Dry Substance of White Corpuscles of Calf. 



Per cent. 



Protein 1.76 



Leuconuclein 68 . 78 



Histon 8 . 76 



Lecithin 7.51 



Fat 4.02 



Cholesterin 4 .40 



Glycogen o . 80 



96.03 



