828 PHYSIOLOGY 



forming alkaline and acid haematoporphyrin respectively. The formula of 

 haematoporphyrin has been given by Nencki and Sieber as C 16 H 18 N 2 3 , 

 and is according to them isomeric with the chief bile-pigment, bilirubin. 

 According to Willstatter its formula is C 33 H 38 N 4 6 . An alcoholic solution 

 of haematoporphyrin acidulated with hydrochloric acid shows two absorption 

 bands : one, the fainter, between C and D, and the other, broader and 

 more denned, midway between D and E. Solutions of alkaline haemato- 

 porphyrin show four absorption bands : a weak band between C and D, 

 another between D and E, a more strongly marked band nearer to E, and 

 a fourth band, darkest of all, between b and F. It will be observed that 

 in the formation of haematoporphyrin from haematin the iron of the latter 

 has been split off by the action of the strong acid. Laidlaw has found 

 that the splitting off of iron occurs much more readily in the absence of 

 oxygen. If reduced haemoglobin be taken, dr defibrinated blood which 

 has been allowed to stand until it is thoroughly reduced, it is sufficient to 

 add 15 per cent, hydrochloric acid in order not only to convert the greater 

 part of the hemoglobin to haematin but to split off the iron of the latter 

 and form haematoporphyrin. Haemotoporphyrin 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 haematoporphyrin is always alkaline 

 haematoporphyrin and gives the spectrum of this body. 



CHEMICAL RELATIONSHIPS OF HAEMATIN. Haamatin, or haamochromogen, 

 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 disinte- 

 gration products we can throw any light on its chemical relationships and on the con- 

 ditions of its formation in the living organism. When haematin 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 4 N, and the other C 8 H 8 O 5 . The first acid is con- 

 verted into the second by the action of alkalies. The relationship of the two haemal inic 

 acids can be represented by the following formulae : 



/ co \ 



; H 7 NH 



\co/ 



COOH COOH 



If, on the other hand, haemin or haematoporphyrin 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, the distillate contains a mixture of substituted pyrroles formerly 

 known as haemopyrroes. The mixture 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 fluorescences. These reactions are also given by urobilin, one of the 

 urinary pigments and the chief pigment of the faeces, as well as by hydrobilirubin, a 

 substance obtained by the action of tin and sulphuric acid on an alcoholic solution of 

 haematin. 



/% 



