OXYH^EMOGLOBLN. 231 



part of the capactity of the pipette. This known quantity of 

 blood is then washed into the bulb of the pipette by drawing up 

 artificial serum to fill the bulb, where the fluids are mixed by 

 shaking about the fine bead contained in the bulb. Some of this 

 mixture is then allowed to pass into a flattened capillary tube of 

 known capacity fixed on a slide, and the number of corpuscles in 

 a given length of this tube at two or three places is carefully 

 counted. The important question, how much oxyhsemoglobin 

 exists in a given sample of blood, can be determined by diluting 

 a drop until the color equals that of a standard solution of known 

 strength. 



CHEMISTRY OF THE COLORING MATTER OF THE BLOOD. 



Of the chemical constituents found in the red blood-corpuscles, 

 the red coloring matter is by far the must 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, Cg^H^Nj^FeSgO^. It is commonly 

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

 rial containing iron, called hsBmatin. 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. 



