86 HANDBOOK OF PHYSIOLOGY. 



which lets through only the red and orange rays; accordingly to the naked 

 eye, the one (reduced haemoglobin solution) appears purple, the other 

 (oxy-haemoglobin solution) red. The deoxidized crystals or their solu- 

 tions quickly absorb oxygen on exposure to the air, becoming scarlet. 

 It 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 haemo- 

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



Action of Gases on Haemoglobin. Carbonic oxide gas, passed 

 through a solution of haemoglobin, causes it to assume a bluish color, 

 and its spectrum to be slightly altered; two bands are still visible, but 

 are slightly nearer the blue end than those of oxy-haemoglobin (see 

 plate). The amount of carbonic oxide taken up is equal to the amount 

 of the oxygen displaced. Although the carbonic oxide gas readily dis- 

 places 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 when breathed, the gas combines with the haemo- 

 globin of the blood, and produces a compound which cannot easily be 

 reduced. This compound (carboxy-haemoglobin) is by no means 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 haemoglobin closely resemble those of oxy- 

 haemoglobin. 



Nitric oxide produces a similar compound to the carbonic-oxide 

 haemoglobin, which is even less easily reduced. 



Nitrous oxide reduces oxy-haemoglobin. 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 

 oxy-haemoglobin, the haemoglobin is reduced and an additional band 

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

 bands of oxy-haemoglobin replace that of reduced haemoglobin, but the 

 band in the red persists. 



Derivatives of Haemoglobin. 



Methaemoglobin. If an aqueous solution of oxy-haemoglobin is ex- 

 posed 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 

 developed. The solution, too, becomes brown and acid in reaction, and 

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

 position of oxy-haemoglobin, and to the production of methc&moglMn 

 On adding ammonium sulphide, reduced haemoglobin is produced, and 

 on shaking this up with air, oxy-haemoglobin is reproduced. Methaemo- 

 globin is probably a stage in the deoxidation of oxy-haemoglobin. It 

 appears to contain less oxygen than oxy-haemoglobin, but more than 

 reduced haemoglobin. Its oxygen is in more stable combination, how- 

 ever, than is the case with the former compound. 



Haematin. By the action of heat, or of acids or alkalies in the 

 presence of oxygen, haemoglobin can be split up into a substance called 

 Hcematin, which contains ^11 the iron of the haemoglobin from which it 



