138 THE BLOOD 



a definite amount of oxygen, see chapter on Respiration. When subjected 

 to a mercurial air-pump the oxgyen is given off, and the crystals become 

 of a purple color. A solution of the oxyhemoglobin in the blood corpuscles 

 may be made to give up oxygen, and to change color in a similar manner. 

 One gram of oxyhemoglobin liberates 1.59 c.c. oxygen, or, according to Hiif- 

 ner's later determinations, i .34 c.c., see page 292. 



This change may be also effected by passing through the solution of 

 blood or of oxyhemoglobin, hydrogen or nitrogen gas, or by the action of 

 reducing agents, of Stokes' s fluid* or ammonium sulphide are the most 

 convenient. 



With the spectroscope, a solution of deoxidized or reduced hemoglobin 

 is found to give an entirely different appearance from that of oxidized hemo- 

 globin. Instead of the two bands at D and E, we find a single broader but 

 fainter band occupying a position midway between the two, and at the same 

 time less of the blue end of the spectrum is absorbed. Even in strong solu- 

 tions this latter appearance is found, thereby differing from the strong solu- 

 tion of oxidized hemoglobin which lets through only the red and orange 

 rays; accordingly, to the naked eye the one (reduced-hemoglobin solution) 

 appears purple, the other (oxyhemoglobin solution) red. The deoxidized 

 crystals or their solutions quickly absorb oxygen on exposure to the air, 

 becoming scarlet. If solutions of blood be taken instead of solutions of 

 hemoglobin, results similar to the whole of the foregoing can be obtained. 



Venous blood never, except in the last stages of asphyxia, fails to show 

 the oxyhemoglobin bands, inasmuch as the greater part of the hemoglobin 

 even in venous blood exists in the more highly oxidized condition. 



Action of Gases on Hemoglobin. Carbonic-oxide gas passed through 

 a solution of hemoglobin causes it to assume a cherry-red color and to 

 present a slightly altered spectrum; two bands are still visible but are 

 slightly nearer the blue end than those of oxyhemoglobin, see Plate I. The 

 amount of carbonic oxide taken up is equal to the amount of the oxygen 

 displaced. Although the carbonic-oxide gas readily displaces oxygen, the 

 reverse is not the case, and upon this property depends the dangerous effect 

 of coal-gas poisioning. Coal gas contains much carbonic oxide, and, when 

 breathed, the gas combines with the hemoglobin of the blood and produces 

 a compound which cannot easily be reduced. This compound (carboxy- 

 hemoglobin) is not an oxygen carrier, and death may result from suffocation 

 due to the want of oxygen, notwithstanding the free entry of pure air into the 

 lungs. Crystals of carbonic-oxide hemoglobin closely resemble in form 

 those of oxyhemoglobin. 



*Stokes's fluid consists of a solution of ferrous sulphate, to which ammonia has been 

 added and sufficient tartaric acid to prevent precipitation. Another reducing agent is a 

 solution of stannous chloride, treated in a way similar to the ferrous sulphate, and a third 

 reagent of like nature is an aqueous solution of yellow ammonium sulphide, NH 4 HS. 



