276 THE BLOOD. 



The constituent of the blood-corpuscles existing in greatest quantity 

 is the red pigment haemoglobin. 



Blood-pigments. 



According to HOPPE-SEYLER the coloring-matter of the red blood- 

 corpuscles is not in a free state, but combined with some other sub- 

 stance. The crystalline coloring-matter, the haemoglobin or oxyhsemo- 

 globin, which may be isolated from the blood, is considered, according 

 to HOPPE-SEYLER, as a cleavage product of this compound, but it acts 

 in many ways unlike the questionable compound itself. This compound 

 is insoluble in water and uncrystallizable. It strongly decomposes 

 hydrogen peroxide without being oxidized itself; it shows a greater resist- 

 ance to certain chemical reagents (as potassium ferricyanide) than the 

 free coloring-matter; and, lastly, it gives off its loosely combined oxygen 

 much more easily in vacuum than the free pigment. To distinguish 

 between the cleavage products, the haemoglobin, and the oxyhaemoglobin, 

 HOPPE-SEYLER calls the compound of the blood-coloring matter of the 

 venous blood-corpuscles phlebin, and that of the arterial arterin. Other 

 investigators, such as H. U. KOBERT and BoHR, 2 the latter calling the 

 pigment of the blood-corpuscles hcemochrom, are of a similar opinion. 

 Since the above-mentioned combinations of the blood-coloring matters 

 with other bodies, for example (if they really do exist) with lecithin, have 

 not been closely studied, the following statements will apply only to the 

 free pigment, the haemoglobin. 



The color of the blood depends in part on kcemoglobin and in part 

 on a molecular combination of this substance with oxygen, the oxy- 

 hamoglobin. We find in blood after asphyxiation almost exclusively 

 haemoglobin, in arterial blood disproportionately large amounts of 

 oxy haemoglobin, and in venous blood a mixture of both. Blood-color- 

 ing matters are also found in striated as well as in certain smooth muscles, 

 and lastly in solution in different invertebrates, although this pigment 

 is not quite identical with that from higher animals. The quantity of 

 haemoglobin in human blood may indeed be somewhat variable under 

 different circumstances, but amounts to about 14 per cent on an average, 

 or 8.5 grams for each kilo of the weight of the body. 



Haemoglobin belongs to the group of compound proteins, and yields 

 as cleavage products, besides very small amounts of volatile fatty acids 

 and other bodies, chiefly a protein globin, and a coloring-matter, hwmo- 



2 Hoppe-Seyler, Zeitschr. f/physiol. Chem., 13, 479; H. U. Robert, Das. Wirbeltier- 

 blut in mikro-kristallogr. Hinsicht, Stuttgart, 1901; Bohr, Centralbl. f. Physiol., 17, 

 p. 688. 



