THE CHEMICAL COMPOSITION OF THE BLOOD 171 



extractives, and salts. The first of these embrace serum-globuUn, 

 serum-albumin, fibrin-ferment and nucleoprotein. 



Blood Serum. — The serum is a sticky liquid, the specific gravity 

 of which varies between 1.027 and 1.032; its average value is 1.028. 

 Toward litmus it exhibits an alkaline reaction which is somewhat 

 greater than that of the plasma. Its color is faintly yellow, shading 

 into green. While clear under ordinary conditions, it may become 

 cloudy or milky in consequence of its admixture with varying amounts 

 of fat. The yellowish coloring material ordinarily present in fats, to 

 which the appearance of the serum is due, is generally called lutein 

 or lipochrome. 



The quantity of the cellular material ordinarily found in serum, varies between 

 7.0 and 9.7 per cent. The bulk of the latter is formed by proteins in amounts of 

 5.5 to 8.4 per cent. The average depression of the freezing point of blood-serum is 

 given as A = -0.526°, as against that of whole blood which is A = -0.537°. The 

 following analytical data pertaining to serum have been supplied by Abderhalden : 



Water 913 . 64 



Solids 86.36 



Protein 72.50 



Sugar 1.05 



Cholesterol. 1 .238 



Lecithin 1 . 675 



Fat : 0.926 



Phosphoric acid as nuclein . 0133 



Soda 4.312 



Potash 0.255 



Iron oxid '. 



Lime 0.1194 



Magnesia . 0446 



Chlorin 3.69 



Phosphoric acid . 244 



Inorganic phosphoric acid . 0847 



The Proteins of the Blood. — Fibrinogen, the mother-substance of 

 fibrin, is associated with serum-globulin and serum-albumin (page 216). 

 Serum-globulin is also called paraglobulin, serum-casein, or fibrino- 

 plastic substance. Besides being present in plasma and serum, it is 

 also found in lymph, transudates and exudates, as well as in the 

 corpuscles and several tissues of the body. The probabihty is that 

 serum-globulin is not a separate substance, but consists of several 

 protein bodies. Their complete separation, however, has not been 

 effected as yet. Hammarsten states that its average composition is : 

 C 52.71, H 7.01, N 1.585, S 1.11, O 23.02. According to Schmiede- 

 berg, its molecular composition is: Cii7Hi82N3oS038+3^H20. The 

 blood of different animals contains different amounts of this substance ; 

 for example, that of the rabbit 1.78 per cent., that of man 3.10 per 

 cent., and that of the horse 4.56 per cent. Serum is said to contain a 

 larger amount of this substance than plasma, the surplus being derived 

 from disintegrated leukocytes. 



The globulins are usually obtained by half-saturation of the serum 



