250 TEXT-BOOK OF PHYSIOLOGY. 



absorption band (see Fig. no), frequently designated as gamma, broader 

 and less marked between the lines D and E, but extending slightly beyond D. 

 Fig. 112 shows in the same graphic manner the increasing breadth of the 

 absorption band with increasing strengths of solution, as well as the simul- 

 taneous 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 converted into oxyhemoglobin, which imparts to the blood or solution 

 a bright red or scarlet color. If the blood or solution be now deprived 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, however, is not due entirely to a fall of 

 pressure but partly to the dissociation 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 dioxid, which lower oxygen pressure, or by the addition of reducing 

 agents, such as ammonium sulphid or Stokes' fluid. 



These experimental determinations of the relation of oxygen to hemo- 

 globin partly explain the oxidation and deoxidation of the hemoglobin in the 

 lungs and tissues. As the blood passes through the lungs and is subjected 

 to the oxygen pressure there, the hemoglobin combines with a definite 

 quantity of oxygen, and on emerging from the lungs exhibits a bright red or 

 scarlet color; as the blood passes through the systemic capillaries where the 

 oxygen pressure in the surrounding tissues is low, the oxyhemoglobin yields 

 up a portion of its oxygen, becoming deoxidized or reduced, and the blood 

 on emerging from the tissues exhibits a dark bluish color. The portion of 

 oxygen given up to the tissues is termed respiratory oxygen. In 100 parts of 

 arterial blood the coloring-matter presents itself almost exclusively in the 

 form of oxyhemoglobin. In passing through the capillaries about 5 per cent, 

 only gives up its oxygen and becomes reduced, so that both kinds are present 

 in venous blood. In asphyxiated blood only reduced hemoglobin is present. 

 It is this capability of combining with and of again yielding up oxygen, that 

 enables hemoglobin to become the carrier of oxygen from the lungs to the 

 tissues. 



Carbon Monoxid Hemoglobin. Carbon monoxid is a constituent of 

 coal-gas and more largely of water-gas. From either source it is likely to 

 accumulate in the air, and if inspired for any length of time produces a series 

 of effects which may eventuate in death. If blood be brought into contact 

 with this gas, it assumes a bright cherry-red color, which is quite persistent 

 and due to the displacement of the loosely combined oxygen and the union 



