CHEMICAL BASIS OF THE ANIMAL BODY. 1297 



haematin (see below). When a solution of hsematin in alkali 

 is reduced with Stokes' fluid 1 or ammonium sulphide the solu- 

 tion obtained shews two absorption bands identical with those 

 already described as characteristic of haemochromogen. From 

 these facts it would at first sight appear that reduced haematin 

 in alkaline solution and haemochromogen in a similar solution 

 are identical substances, and this is the view which has been 

 most generally adopted. Solutions of haemochromogen show 

 a very strong absorption band in the extreme violet between 

 h and 6r, its centre corresponding to w. L. 420. By appro- 

 priate methods hsemochromogen may be obtained in a crystal- 

 line form. 



9. Hgematin. C 32 H 32 N 4 FeO 4 (?). 



When oxy-haemoglobin is decomposed by either acids or 

 alkalis it yields a proteid and a coloured substance known as 

 haematin. This decomposition may take place in old blood- 

 clots or extravasations and is readily produced by the action 

 of either gastric or pancreatic juice on oxy-haemaglobin, so that 

 haematin is frequently found in the contents of the alimentary 

 canal and in the faeces, more especially with a flesh diet. It 

 has also been found in urine as the result of poisoning with sul- 

 phuric acid or arseniuretted hydrogen. 



For ordinary purposes haematin is characterized chiefly by 

 the spectroscopic appearances of its solutions. When dissolved 

 in an alkali (ammonia) it shews one absorption band in the 

 veliow adjoining D to the red side of this line, while at the 

 same time there is great absorption at the blue end of the spec- 

 trum (Fig. 90, Nos. 1 and 2). On treatment with a reducing 

 agent, Stokes' fluid or ammonium sulphide, this band is replaced 

 by two others in the green of which the one nearest D is remark- 

 ably dense, the other less sharply defined. Very little absorp- 

 tion of the red end is observed while that of the blue is as before 

 very marked (Fig. 90, No. 3). This is the spectrum of reduced 

 hsematin and is identical with that of haemochromogen. Alka- 

 line solutions of haematin are strongly dichroic, being ruby-red 

 in thick layers and greenish in thin layers viewed by reflected 

 light. 



The acid alcoholic solution of haematin is characterized by 

 one absorption band between Q and D, adjoining C, whose 

 centre is situated at w. L. 640. This band is somewhat similar 

 to that of methsemoglobin, but it is less dense, and careful obser- 

 vation shews that the centres of the respective bands do not 

 coincide (Fig. 90, Nos. 5 and 4). Acid solutions of haematin 

 are monochromatic and of a dull reddish-brown colour. If 



1 Prepared by adding tartaric acid to a solution of ferrous sulphate and 

 then ammonia until it is strongly alkaline. 



82 



