THE BLOOD 251 



tion be now deprived of oxygen, the oxyhemoglobin is converted into reduced 

 hemoglobin, which imparts to the blood or solution a dark bluish-red or pur- 

 ple color. 



The quantity of oxygen absorbed by i gram of hemoglobin is estimated 

 at 1.56 c.c. measured at oC. 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 

 of the carbon monoxid with the hemoglobin. The compound thus formed 

 is very stable and resists the action of various reducing agents. The passage 

 of air or of some neutral gas through the blood for a long period of time will 

 gradually displace the carbon monoxid and enable the hemoglobin again to 

 absorb oxygen. It is for this reason that partial poisoning with the gas is 

 not fatal. It is to its power of displacing oxygen and forming a stable com- 

 pound with hemoglobin and thus interfering with its respiratory function 

 that carbon monoxid owes its poisonous properties. Examined spectro- 

 scopically, solutions of carbon monoxid hemoglobin exhibit two absorption 

 bands closely resembling in position and extent those of oxyhemoglobin; but 

 careful examination shows that they are slightly nearer the violet end of the 

 spectrum and closer together. (See Fig. 101.) A useful test for CO blood 

 is the addition of caustic soda, which produces a cinnabar red precipitate. 



