7u [ AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



haemochromogen, which is a crystallizable cleavage-product of haemoglobin. According 

 to Hoppe-Seyler the oxygen in oxyhaemoglobin is bound to the haemochromogen group. 

 Haemochromogen treated with a strong dehydrating agent is converted, with elimination 

 of iron, into Jioematoporphyrin, Ci 6 H, 8 N.,0 3 , an isomer of bilirubin. Haematoporphyrin 



is said to occur in normal urine. 1 Haematoporphyrin treated with nascent hydrogen is 

 converted into a body believed to be identical with hydro- or urobilirubin. Analogous to 

 this is the work of the liver in the body, manufacturing the biliary coloring matter from 

 haemoglobin, and retaining the separated iron for the synthesis of fresh haemoglobin 

 (see p. 5i29). Hcematoidin, found in old blood-stains, is believed to be identical with 

 bilirubin. 



The Bile-pigments. — The ordinary coloring matter of yellow human bile is bilirubin, 

 C ; JI: iB N 4 6 . The next higher oxidation-product is the green bit inn I in, C 32 H 36 N t O fe , 

 which is the usual dominant color in the bile of herbivora. These coloring-matters and 

 others derived from them have been found in gall-stones. Jolles 2 gives the following 

 products of the oxidation of bilirubin: 



Bilirubin (red) t' 16 H I8 X 2 3 ; 



Biliverdin (green) C 16 H ls N 2 O i ; 

 Bilicyanin (blue) ? 



— - — (violet) ? 



(red) ? 



(brown) ? 



Bilixanthin (brownish-yellow) C 16 H 18 N 2 0». 



If nitric acid containing a little nitrous acid be added to a solution ol bilirubin, a play of 

 colors is observed at the juncture of the two fluids, undoubtedly depending upon various 

 st; i -es of oxidation. Above is a ring of green (biliverdin), then blue and violet (bilicya- 

 nin), red, yellowish-brown (bilixanthin). Bilixanthin (= choletelin) is the highest oxida- 

 tion-product. The above is known as Gmelins test. 3 



If bilirubin or biliverdin is subjected to the action either of nascent hydrogen or 

 of putrefaction it is reduced to hydrobilirubin, C 32 H u N 4 7 . This substance is therefore 

 formed in the intestinal tract, is in part absorbed, and appears in the urine, where it is 

 called urobilin, though the two are identical. Urobilin gives a yellowish coloration to the 

 urine. Injection into the blood-vessels of distilled water, ether, chloroform, the biliary 

 salts, or arsenuretted hydrogen, produces a solution of the red blood-corpuscles and conver- 

 sion of haemoglobin into biliary coloring matters which are thrown out in the urine. Bili- 

 rubin, biliverdin, and bilicyanin give characteristic spectra. 



Melanins. — Under this name are classed the pigments of the skin, of the retina, and 

 of the iris. In melanosis and kindred diseases they are deposited in black granules. 

 Abel and Davis 1 prepared pure pigment from the skin of the negro and find that it con- 

 tains no iron and 1.5 per cent, of sulphur. These pigments arise from proteid. On 

 decomposition they yield two melaninic acids. 5 



Tryptophan. — This is said to be a cleavage-product of hemipeptone in tryptic diges- 

 tion ; 6 it gives a red color with chlorine and a violet color with bromine, due to halogen- 

 addition compounds. 



Lipochromes. — These include lutein, the yellow pigment of the corpus luteum, of 



1 Gar rod: Journal of Physiology, 1894, vol. 17, p. 348. 



2 Pilii./.rs Archiv, 1899, Bd. 75, S. 446. 



5 For a delicate modification of this test see Jolles: Zeitschrift fur physiologische Chemie, 1895, 

 Bd. 20, S. 461. 



4 Journal of Experimental Medicine, 1896, vol. i. p. 361. 

 1 . 1 ones: American Journal of Physiology, 1899, vol. ii. p. 380. 

 delmann: Zeitschrift fur Biologie, 1890, Bd. 26, 8. 491. 



