2l6 PHYSIOLOGICAL CHEMISTRY. 



sodium salts was found in the plasma, while the potassium 

 salts were found largely in the corpuscles. The calcium and 

 magnesium salts occur mainly in the plasma. In the blood 

 the excess of alkali shown exists probably mainly as carbon- 

 ate. All analyses seem to indicate a difference between the 

 blood of men and women. The male blood is richer in solids. 

 The female blood on the other hand appears to be slightly 

 richer in the mineral salts. 



Blood is characterized particularly by the peculiar compound 

 containing iron present, known as hemoglobin. Many of the 

 tests for the recognition or identification of blood depend on 

 this substance, which is found nowhere else. As a whole 

 blood is distinguished by the phenomenon of coagulation which 

 is connected with the fibrin present. Because of the great im- 

 portance of this phenomenon it will be briefly discussed here; 

 the details of the subject belong to physiology rather than to 

 chemistry and are not yet sufficiently worked out for clear 

 elementary presentation. 



FIBRIN AND THE COAGULATION OF BLOOD. 



As has been already pointed out fibrin is the product result- 

 ing from a certain reaction in which a forerunner or parent 

 substance called fibrinogen is concerned. As it exists in the 

 blood vessels normally this fibrinogen is soluble and stable, but 

 when the vessel is pierced and the contents allowed to come in 

 contact with the air the soluble fibrinogen becomes the insolu- 

 ble fibrin, which is the well-known stringy substance described 

 in an earlier chapter. A great deal has been written on the 

 subject of this spontaneous coagulation, which is now gener- 

 ally believed to be brought about by the action of a peculiar 

 ferment formed by the breaking down of the white blood cor- 

 puscles. From these cells it appears that a special zymogen 

 which has been called prothrombin is first formed ; this in the 

 presence of calcium salts yields the true fibrin ferment or en- 

 zyme called thrombin. It may be easily shown that the addi- 

 tion of ammonium oxalate or some other precipitant of cal- 



