THE BLOOD. 93 



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

 strong solutions this latter appearance is found, thereby differing from 

 the strong solution of oxidized haemoglobin which lets through only the 

 red and orange rays; accordingly to the naked eye the one (reduced 

 haemoglobin solution) appears purple, the other (oxy-hsemoglobin solu- 

 tion) red. The deoxidized crystals or their solutions quickly absorb oxy- 

 gen on exposure to the air, becoming scarlet. If solutions of blood be 

 taken instead of solutions of haemoglobin, 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 oxy-haemoglobin bands, inasmuch as the greater part of the 

 haemoglobin even in venous blood exists in the more highly oxidized 

 condition. 



Action of Gases on Haemoglobin. Carbonic oxide, passed through 

 a solution of haemoglobin, causes it to assume a bluish color, and the spec- 

 trum is slightly altered; two bands are still visible, but are somewhat 

 nearer the blue end than those of oxy-haemoglobin (see Plate). The 

 amount of carbonic oxide 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 poisoning. Coal gas contains much carbonic oxide, and this at once, 

 when breathed, combines with the haemoglobin of the blood, producing 

 a compound which cannot easily be reduced, and since it is by no means 

 an oxygen carrier, death may result from suffocation from want of oxygen 

 notwithstanding the free entry into the lungs of pure air. Crystals of 

 carbonic-oxide haemoglobin closely resemble those of oxyhaemoglobin. 



Nitric oxide produces a similar compound to the carbonic-oxide haemo- 

 globin, which is even less easily reduced. 



Nitrous oxide reduces oxyhaemoglobin, and therefore leaves the reduced 

 haemoglobin in a condition to actively take up oxygen. 



Sulphuretted Hydrogen. If this gas be passed through a solution of 

 oxyhaemoglobin, the haemoglobin is reduced and an additional band 

 appears in the red. If the solution be then shaken with air, the two 

 bands of oxyhaemoglobin replace that of reduced haemoglobin, but the 

 band in the red persists. 



PRODUCTS OF THE DECOMPOSITION OF HAEMOGLOBIN. 



Methaemoglobin. If an aqueous solution of oxyhaemoglobin be 

 exposed to the air for some time, its spectrum undergoes a change; the 

 two D and E bands become faint, and a new line in the red at c is devel- 

 oped. The solution, too, has become brown and acid in reaction, and is 

 precipitable by basic lead acetate. This change is due to the decomposi- 

 tion of haemoglobin, and to the production of metlicernoglobin. On add- 



