238 ILEMATOPOKPHYKIK 



however further regarded as derived by dehydration from a true hoema- 

 toporphyrin whose composition is Ci 6 H 18 N 2 8 . The latter is thus 

 identical in composition with bilirubin, whose formula is undoubtedly 

 C 16 H 18 N 2 8 . This is regarded as affording the desired chemical proof 

 of the genetic relationship of the bile- and blood-pigments, the deri- 

 vation of the former from haematin being represented as follows, 

 C 82 H 82 N 4 Fe0 4 + 2H 2 Fe = 2 (C 16 H 18 N 2 3 ) . 



12. Haematoporphyrin. 1 C 68 H 74 N 8 12 (?). (Iron-free hsematin.) 



If haematin is dissolved in concentrated sulphuric acid it yields 

 a solution which, after nitration through asbestos, is of a brilliant 

 purple-red colour. By the action of the acid, the iron is removed 

 from the haematin and haematoporphyrin is formed. 2 If this solu- 

 tion is diluted with sulphuric acid it shows with a spectroscope 

 two absorption bands of which one adjoins D to the red side of 

 this line, while the other is very strongly marked and lies midway 

 between D and E. By the addition of water to the solution in 

 sulphuric acid the colouring matter is largely precipitated, especi- 

 ally if some alkali be carefully added to neutralise the acid. The 

 precipitate thus obtained is readily soluble in dilute alkalis, and 

 this solution is characterised by four absorption bands, one half- 

 way between C and D, two between D and E, and one conspicuous 

 band adjoining b and extending nearly to F. 3 Haematin also yields 

 haamatoporphyrin by the action of strong hydrochloric acid at 130 

 in sealed tubes. 



Some interest attaches to this substance owing to its occasional 

 occurrence in urine in forms which show slightly different absorp- 

 tion spectra but are probably closely related if not identical. 

 Thus it occurs as urohasmatin or urohsematoporphyrin, 4 or as 

 ordinary haematoporphyrin. 5 It is also found in the integument 

 of some invertebrates 6 and in the egg-shells of certain birds. 7 It 

 is further interesting to notice that in haematoporphyrin we have a 

 strongly coloured pigment derived from hsematin with removal of 

 the iron which the latter contains, a fact which facilitates our con- 

 ception of a possible derivation of the iron-free bile-pigments 

 from the iron-containing haemoglobin or haematin. This relation- 

 ship will be more fully discussed when the bile-pigments are 

 described. 



1 Hoppe-Seyler, Med.-chem. Unters. Hft. 4. 1871, S. 528. 



2 In the absence of oxygen a substance called by Hoppe-Seyler hcematolin is 

 obtained, C 68 H 78 F 8 O 7 . 



3 These spectra are figured in Halliburton, Chem. Physiol. and Pathol. Fig. 59, 

 p. 277, Nos. 10 and 11. 



* MacMunn, Proc. Roy. Soc. Vol. xxxi. 1880, p. 206, Jl. of Physiol. Vols. vi. 

 (1884), p. 36, x. (1889), p. 71, Clinical Chem. of Urine, 1889, p. 109,' Proc. Physiol. 

 Soc. No. iv. 1890. See Jl. of Physiol. Vol. xi. (1890), p. xiii. 



5 E. Salkowski, Zt. f. physiol. Chem. Bd. xv. (1891), S. 286. 



B MacMunn, Jl. of Physiol. Vols. vn. (1885), p. 240, vm. p. 384. 



7 For literature see MacMunn, Jl. of Physiol. Vol. vu. p. 251. 



