THE BLOOD. 



251 



manner the increasing breadth of the absorption band with increas- 

 ing strengths of solution, as well as the simultaneous absorption of 

 light at both the red and violet ends of the spectrum. 

 , Compounds of Hemoglobin. The coloring-matter of the\ 

 ( blood is characterized by the property of combining with and of\ 

 \again yielding up oxygen. The union is a chemic one, taking place 

 under certain pressure conditions. It therefore may exist in two 

 states of oxidation, distinguished by a difference in color and their 

 absorption spectra. If hemoglobin either in blood or in solution 

 be shaken with air, it at once combines with oxygen and is con- 

 verted into oxyhemoglobin, which imparts to the blood or solution a 

 bright red or scarlet color. If the blood or solution be now deprived 



FIG. 107. GRAPHIC REPRESENTATION 

 or THE ABSORPTION OF LIGHT IN 

 A SPECTRUM BY SOLUTIONS OF 

 OXYHEMOGLOBIN OF DIFFERENT 

 STRENGTHS. The shading indi- 

 cates the amount of absorption of 

 the spectrum, and the numbers at 

 the side the strength of the solu- 

 tion. 



FIG. 108. GRAPHIC REPRESENTATION 

 OF THE ABSORPTION OF LIGHT 

 IN A SPECTRUM BY SOLUTIONS 

 OF HEMOGLOBIN OF DIFFERENT 

 STRENGTHS. The shading indi- 

 cates the amount of absorption of 

 the spectrum, and the numbers at 

 the side the strength of the solu- 

 tion. 



of oxygen, the oxyhemoglobin is converted into reduced hemoglobin, 

 which imparts to the blood or solution a dark bluish or purple color. 

 The quantity of oxygen absorbed by i gram of hemoglobin is 

 estimated at 1.56 c.c. measured at o C. and 760 mm. of mercury. 

 The compound formed by the union of oxygen and hemoglobin is a 

 very feeble one; for when the pressure is lowered the union becomes 

 less stable, and as the zero point is approached, as in the Torricellian 

 vacuum, a rapid dissociation of the oxygen takes place. This, how- 

 ever, is not due entirely to a fall of pressure but partly to the dis- 

 sociating force of heat, which increases in power as the pressure falls. 

 The same dissociation of oxygen can be brought about by passing 

 through blood indifferent gases, such as hydrogen, nitrogen, carbon 



