318 THE BLOOD. 



together with the fibrin, and accordingly lower values are found 

 in the serum than in the plasma. 



An idea of the mineral constituents of the serum, and their 

 quantitative relations, may be had from the accompanying table : 



Man. 



Potassium oxide 0.387 0.401 pro mille. 



Sodium oxide 4.290 " 



Chlorine 3.5653.659 



Calcium oxide 0.155 " 



Magnesium oxide 0.101 " 



From this it will be seen that sodium in the form of the chloride 

 largely predominates in the serum, while potassium occurs only in 

 small amounts. This is exactly the reverse of what is seen in the 

 morphological elements of the body, of which potassium compounds 

 are the principal salts present. It is noteworthy, moreover, that the 

 amount of sodium chloride is practically constant in the blood, no 

 matter whether large quantities are ingested or the salt is given in only 

 small amounts. During starvation even, or when the potassium salt 

 is artificially substituted, the amount present in the blood remains 

 practically constant. Apparently it occurs only in solution, and does 

 not form an integral part of the albuminous molecule, as is the case 

 with the phosphates of the blood. Of these, traces only are present 

 in solution, while the greater portion is more or less intimately com- 

 bined with the albumins. As the lecithins which are found in the 

 blood also contain phosphorus, it follows that these figures, which are 

 obtained by incinerating a given amount of serum or plasma and 

 determining the phosphoric acid in the ash, are too high. In serum 

 which had been freed from lecithin Sertoli and Mroczkowski found 

 amounts varying between 0.02 and 0.09 pro mille, calculated as di- 

 sodium phosphate. In the estimation of the sulphates we meet 

 with still greater difficulties, as the sulphur of the albumins is 

 included in the determination. The amount which is present in 

 solution, however, is certainly very small. The iron which is at 

 times met with in the serum is unquestionably derived from the 

 leucocytes, and is an accidental constituent. The amount which 

 may be obtained is always exceedingly small. 



Of other elements, traces of silicon, fluorine, copper, and man- 

 ganese have at times been observed. 



The coloring-matter of the serum and plasma is supposedly due 

 to a substance belonging to the class of lipochromes or lutei'ns. 



The albumins ef the serum which also occur in the plasma, viz., 

 serum-albumin and serum-globulin, have been considered. Of the 

 fibrinoglobulin which is formed during coagulation of the blood, 

 and which is thought to result from decomposition of fibrinogen, 

 comparatively little is known. It coagulates at 64 C., and appar- 

 ently represents about one-third of the fibrinogen molecule. Of the 

 so-called cell-globulin, still less is known, and both are found only 

 in traces. More important is the presence of the fibrin ferment, 



