PORPHYRINS , 17 



is soluble in alkali, but it is extremely insoluble in acid ; the addition 

 of acid therefore to the alkaline solution produces immediate precipita- 

 tion. On the other hand, if acid be added to oxyhaemoglobin, a brown 

 solution is obtained to which the name "acid hsematin" has always 

 been given. It would appear that the preparation is a solution in 

 appearance only; it is really a suspension, the hsematin being pre- 

 vented, according to Keilin, from forming a gross precipitate by the 

 protective action of the protein in which it is suspended. An exactly 

 similar solution may be made from the base. If the haematin be 

 dissolved in alkali, and to the solution a sufficient amount of gum 

 arabic, gelatine or potassium silicate be added, then, on acidifica- 

 tion, a suspension is formed which shows no tendency to precipitate 

 and which gives a spectrum identical with that of the acid haematin 

 made from oxyhsemoglobin. 



With these phenomena in our minds we shall be in a stronger 

 position to understand the nature of haemoglobin and its related 

 bodies. We must, however, undertake another preliminary enquiry, 

 namely, one into the nature of haemochromogen. 



REFERENCES 



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1918. 



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(4) Fischer, H. and his collaborators. Numerous studies published in the Zeitsch. 



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(5) Hill, R. and Holden, H. F. Biochem. Journ. xx. 1326. 1926. 



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