238 MANUAL OF PHYSIOLOGY. 



CHEMISTRY OF THE COLORING MATTER OF THE BLOOD. 

 Of the chemical constituents found in the red blood corpuscles, 

 the rqd coloring matter is by far the most important. To it alone 

 the blood owes one of its most important functions the respira- 

 tory. 



Oxyhcemoglobin is a chemical compound of great complexity, 

 and of which the percentage composition is given as : 



Carbon, 53.85 



Hydrogen, 7.32 



Nitrogen, 16.17 



Oxygen, 21.84 



Sulphur, 39 



Iron 43 



Its rational formula is unknown, but the following has been 

 proposed as approximate, CeooHgeoN^FeSaOng. It is commonly 

 regarded as a form of globulin, associated with a colored mate- 

 rial containing iron, called haematin. Its chief peculiarities are 

 (1) that, although it contains a colloid substance, it crystallizes 

 more or less readily in all vertebrates when removed from the 

 stroma of the corpuscles ; (2) the considerable amount of iron it 

 contains (0.4 per cent.) ; (3) the remarkable manner in which it 

 is combined with oxygen to form an unstable compound ; and (4) 

 the ease with which it yields its oxygen to the tissues and takes 

 it from the air. 



The readiness with which the oxyhcemoglobin crystals are formed 

 varies much in different animals and under different circum- 

 stances, as may be seen from the following list : 



Most readily guinea pig, rat, mouse. 



Keadily cat, dog, horse, man, ape, rabbit. 



With difficulty sheep, cow, pig. 



Not at all frog. 



The presence of oxygen causes the crystals to form more rapidly, 

 so that a stream of oxygen passed through a strong solution of 

 haemoglobin causes small crystals of oxyhsemoglobin to form. 



The crystals always belong to the rhombic system, being most 

 commonly plates (man, etc.) and prisms (cat), and rarely tetra- 

 hedra (guinea pig) and hexagonal plates (squirrel). 



