936 PHYSIOLOGY 



acid in order not only to convert the greater part of the haemoglobin to 

 hsematin but to split off the iron of the latter and form hsemato- 

 porphyrin. Heematoporphyrin occurs in minute quantities in normal 

 urine and in larger quantities in certain toxic conditions, especially in 

 poisoning by sulphonal, when the urine may have a bright purple 

 colour. It is important to remember that although urine is acid 

 from the presence of acid sodium phosphate, urinary hsemato- 

 porphyrin is always alkaline hsematoporphyrin and gives the spectrum 

 of this body. 



CHEMICAL RELATIONSHIPS OF H^MATIN. Hfematin, or the reduced 

 haemochromogen, is widely diffused through the animal kingdom, occurring in 

 the form of haemoglobin in a large number of the invertebrata, as well as in all 

 the vertebrata except, perhaps, Amphioxus. Since the respiratory function of 

 haemoglobin depends on the power of its iron-containing radical to combine with 

 a molecule of oxygen, forming an easily dissociable compound, it becomes of 

 interest to try whether by a study of its disintegration products we can throw 

 any light on its chemical relationships and on the conditions of its formation in 

 the living organism. When hsematin is oxidised with sodium bichromate and 

 acetic acid two new acids are formed, called the haematinic acids. One of these 

 has the formula C 8 H 9 O 4 N, and the other C 8 H 8 O 5 . The first acid is converted 

 into the second by the action of alkalies. The relationship of the two hsematinic 

 acids can be represented by the following formulae : 



.CO / C0 \ 



C 5 H 7 < >0 C 5 H 7 NH 



COOH COOH 



If, on the other hand, haemin or hgematoporphyrin be reduced by the action of 

 hydriodic acid dissolved in acetic acid with the addition of phosphonium iodide, 

 and the product be distilled with steam, a substance is obtained in the distillate 

 which is hgemopyrrol, and has the formula C 8 H 13 N. Hsemopyrrol readily 

 oxidises to a red substance on exposure to the air. If ammonia be added to the 

 coloured solution the colour changes to yellow, which, on the addition of an 

 ammoniacal solution of zinc chloride, changes to pink with a green fluorescence. 

 These reactions ai e also given by urobilin, one of the urinary pigments and the 

 chief pigment of 1 he faeces, as well as by hydrobilirubin, a substance obtained 

 by the action of tin and sulphuric acid on an alcoholic solution of haematin. 

 Haemopyrrol has been shown by Nencki and Zaleski to have the formula : 



H.3 C C - C 03 M 7 



II II 

 HC CH 



\/ 

 NH 



i.e. it is methyl propylpyrrol. 



The same substance, haemopyrrol, can be obtained from chlorophyll, the green 

 colouring-matter of plants. Chlorophyll, on treatment with strong acid, is 

 converted into phyllocyanin, and then into phyllothaonin. The latter, on 

 treatment with alcoholic caustic soda in sealed tubes at 190 C., yields a sub- 

 stance called phylloporphyrin, which has a purple colour and gives an absorption 

 spectrum similar to that of haematoporphyrin. The close relationship of the 

 two is shown by their formulae : 



