THE CHEMISTRY OF THE ANIMAL BODY. 1015 



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 hcematoporphyrin, G^H^^, 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. 973). 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^ 

 CsjHsgN^g. The next higher oxidation-product is the green biliverdin, Os-jR^N^, 

 which is the usual dominant color in the bile of herbivora. In gall-stones have been found 

 the following coloring matters, to which have been ascribed the accompanying formulae : 



Bilirubin (red), CsaU^N^ ; 



Biliverdin (green), Cs^^N^s; 



Bilifuscin (brown), CsjH^N^g; 



Biliprasin (green), C 32 H a N 4 12 ; 

 Bilihumin (brown), ? 



Bilicyanin (blue), ? 



Choletelin (black), CszH^NAz. 



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

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

 stages of oxidation. Above is a ring of green (biliverdin), then blue and violet (bilicya- 

 nin), red, yellowish-brown (choletelin). Cholotelin is the highest oxidation-product. The 

 above is known as Gmelins test." 1 



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

 of putrefaction it is reduced to hydrobilirubin, C3 2 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 (see 

 p. 988). Bilirubin, biliverdin, and bilicyanin give characteristic spectra. 



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

 of the iris. They contain iron, and their source has been attributed to haemoglobin. In 

 melanosis and kindred diseases they are deposited in black granules. There are melanins 

 of different composition. In a case of melanotic sarcoma the haemoglobin was one quar- 

 ter, the number of blood-corpuscles one-half, the normal, indicating perhaps the source 

 of melanin. 3 



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

 tion ; 4 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 

 blood-plasma, butter, egg-yolk, and of fat ; likewise visual purple of the retina, which is 

 bleached by light. Solutions of the pure visual purple from rabbits or dogs become clear 

 as water on exposure to light. 5 



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



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

 Bd. 20, p. 461. 



3 Brandl und Pfeiffer : Zeitsckrift fur Biologic, 1890, Bd. 26, p. 348. 



4 Stadelmann : Ibid., 1890, Bd. 26, p. 491. * Kiihne : Ibid., 1895, Bd. 32, p. 26. 



