25 2 TEXT-BOOK OF PHYSIOLOGY. 



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 

 hemoglobin 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 hemoglo- 

 bin 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 por- 

 tion 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 asphyx- 

 iated blood only reduced hemoglobin is present. It is this capa- 

 bility 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 con- 

 stituent of both coal-gas and 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 to again 

 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 form- 

 ing a stable compound with hemoglobin and thus interfering with 

 its respiratory function that carbon monoxid owes its poisonous 

 properties^ Examined spectroscopically, "solutions of carbon mon- 

 oxid hemoglobin exhibit two absorption bands closely resembling 

 in position and extent those of oxyhemoglobin; but careful examina- 

 tion shows that they are slightly nearer the violet end of the spectrum 

 and closer together. (See Fig. 106.) A useful test for CO blood 

 is the addition of caustic soda, which produces a cinnabar red pre- 

 cipitate. 



Methemoglobin. This is a pigment, closely related to oxy- 

 hemoglobin, found in the blood after the administration of various 



