830 PHYSIOLOGY 



Keduced haemoglobin is a compound of hsembchromogen and a protein, 

 globin. The splitting off of the prosthetic chromatogenic group hsemo- 

 chromogen can be effected either by acid or alkali. When the latter is 

 employed we obtain a red solution which is fairly stable, and can be con- 

 verted by shaking up with air into ordinary alkaline haematin. With acids 

 the decomposition is easily carried further. Even with 2 per cent, hydro- 

 chloric acid a certain amount of haematoporphyrin is formed, and if the 

 strength of the acid be increased to 15 per cent, the whole of the iron is 

 split off and the ha3mochromogen is converted entirely into haemato- 

 porphyrin. 



If oxyhaBmoglobin be treated in the same way it yields acid or alkaline 

 haematin directly, so that ha3matin must be regarded as an oxyhaemo- 

 chromogen. The distinction drawn by Hoppe-Seyler between haemo- 

 chromogen and reduced alkaline haematin had its chief ground in the fact 

 that pure haematin is not reduced to haemochromogen by the action of 

 such reducing agents as ammonium sulphide. The conversion can, how- 

 ever, be easily effected by using a strong reducing agent, such as hydrazine 

 hydrate. Whether the haematin contains the whole of the oxygen of the 

 oxyhaBmoglobin is doubtful. According to Ham and Balean, when 

 oxyhaBmoglobin is converted by means of acids into acid haematin, exactly 

 half of the oxygen of the oxyhaBmoglobin is given off, so that haematin 

 would only contain one-half of the oxygen of the oxyhaBmoglobin. There 

 is a marked difference between the stability of haematin and haBmochromogen. 

 In the oxidised form of haematin the iron is firmly bound and can only be 

 split off by using strong sulphuric acid, concentrated hydrochloric acid 

 being insufficient for the purpose. 



It has been shown by Laidlaw that the change in the reverse direction, 

 i.e. the combination of iron with haBmatoporphyrin to form haBmochromogen, 

 may be effected with equal ease. One gramme haBmatoporphyrin prepared 

 by Nencki's method is dissolved in dilute ammonia and warmed in a flask 

 on the water-bath. Some Stokes's fluid, prepared from about 2 grm. 

 ferrous sulphate, and a few drops of a 50 per cent, hydrazine hydrate 

 solution are added. At the end of one or two hours the solution is seen 

 to be of a bright red colour when examined in thin layers, and on dilution 

 shows the typical absorption spectrum of haBmochromogen, which changes 

 to that of alkaline haematin on shaking with air. Strong potash is added, 

 and the ammonia is boiled off in an evaporating dish with free exposure 

 to the air. The hydrazine is decomposed, and a solution of haematin 

 remains, and can be precipitated by acidification with hydrochloric acid. 

 The pigment obtained in this way agrees in every respect with that prepared 

 from oxyhaBmoglobin. Analysis of the product gave 9-58 per cent, of iron, 

 which agrees with Nencki's formula for haematin, C 32 H 30 N 4 3 Fe. 



A pigment occurring in the wing feathers of certain birds, called turacin, was shown 

 by Church to contain copper, and to yield, on treatment with strong sulphuric acid, 

 a substance indistinguishable from hsematoporphyrin. Laidlaw has succeeded in 

 synthetising this pigment by treating ordinary heematoporphyrin obtained from blood 



