CHEMICAL BASIS OF THE ANIMAL BODY. 239 



identical in composition with bilirubin whose formula is undoubtedly C 16 H 18 N 2 3 . 

 This is regarded as affording the desired chemical proof of the genetic relationship 

 of the bile- and blood-pigments, the derivation of the former from haematin being 

 represented as follows, C 32 H 32 N 4 Fe0 4 + 2H 2 - Fe = 2 (C 16 H 18 N 2 3 ). 



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

 If haematin is dissolved in concentrated sulphuric acid it yields a 



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

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

 from the hsematin and haematoporphyrin is formed 2 . If this solution 

 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, especially 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 Z>, two between D 

 and E, and one conspicuous band adjoining b and extending nearly to 

 F. 3 Haematin also yields hsematoporphyrin 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 absorption 

 spectra but are probably closely related if not identical. Thus it occurs as 

 urohaematin or urohaematoporphyrin 4 , or as ordinary hsematoporphyrin 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 

 haematin with removal of the iron which the latter contains, a fact 

 which facilitates our conception of a possible derivation of the iron-free 

 bile pigments from the iron-containing haemoglobin or haematin. This 

 relationship will be more fully discussed when the bile pigments are 

 described. 



13. Hsematoidin 8 . C 16 H I8 N 2 O 3 . 



This substance is found as reddish or orange rhombohedral crystals 



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



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

 obtained, C 68 H 78 F S 7 . 



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

 p. 277, Nos. 10 and 11. 



4 MacMunn, Proc. Boy. 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. 



6 MacMunn, JL of Physiol. Vols. vn. (1885), p. 240, vin. p. 384. 



7 For literature see MacMunn, JL of Physiol. Vol. vn. p. 251. 



8 The literature of this substance is very fully quoted in Hermann's Hdbch. d. 

 Physiol. Bd. v. Th. 1, S. 245. 



