TETRONERYTHRIN, CARMINIC ACID. 795 



above, we tend more and more to accept the view that the melanins are 

 derived from the cyclic components of the proteins. 



In addition to the coloring matters of the human skin it is in place here to 

 treat of the pigments found in the skin or epidermal formation of animals. 



The beautiful color of the feathers of many birds depends in certain cases on 

 purely physical causes (interference-phenomena), but in other cases on coloring 

 matters of various kinds. Such a coloring matter is the amorphous reddish-violet 

 turacin, which contains 7 per cent copper and whose spectrum is very similar to 

 that of oxyha3moglobin. It must- be remarked that according to LAIDLAW ! 

 turacin or at least a pigment with the same properties can be obtained on boiling 

 haematoporphyrin in dilute ammonia with ammoniacal copper solution. KRUKEN- 

 BERG 2 found a large number of coloring matters in birds' feathers, namely, zooery- 

 thrin, zoofuhin, turacoverdin, zoorubin, psittacofulvin, and others which cannot be 

 enumerated here. 



Tetronerythrin, so named by WTJRM, is a red amorphous pigment which is 

 soluble in alcohol and ether, and which occurs in the red warty spots over the eyes 

 of the heathcock and the grouse, and which is very widely spread among the inver- 

 tebrates (HALLIBURTON, DE MER.E.TKOWSKI, MACMUNN). Besides tetronerythrin 

 MACMUNN found in the shells of' crabs and lobsters a blue coloring matter cyano- 

 crystallin, which turns red with acids and by boiling water. Hcematoporphyrin, 

 according to MAcMuNN, 3 also occurs in the integuments of certain of the lower 

 animals. , 



In certain butterflies (the pieridinae) the white pigment of the wings consists, 

 as shown by HOPKINS/ of uric acid, and the yellow pigment of a uric-acid deriva- 

 tive, lepidotic acid, which yields a purple substance, lepidoporphyrin, on warming 

 with dilute sulphuric acid. The yellow and red pigment of the Vanessa are, 

 according to LINDEN, 5 of an entirely different kind. In this case we are dealing 

 with a compound between protein and a pigment which is allied to bilirubin or 

 urobilin, i.e., a compound similar to haemoglobin. 



In addition to the coloring matters thus far mentioned a few others found in 

 certain animals (though not in the skin) will be spoken of. 



Carminic acid, or the red pigment of the cochineal, gives on oxidation, accord- 

 ing to LIEBERMANN and VoswiNCKEL, 6 cochenillic acid, C 10 H 8 O 7 , and coccinic acid. 

 C 9 H 8 O 5 , the first being the tri-carboxylic acid, and the other the di-carboxylic 

 acid, of m-cresol. The beautiful purple solution of ammonium carminate has two 

 absorption-bands between D and E which are similar to those of oxy haemoglobin. 

 These bands lie nearer to E and closer together and are less sharply defined. Pur- 

 ple is the evaporated residue from the purple-violet secretion, caused by the action 

 of the sunlight, upon the so-called " purple gland " of the mantle of certain species 

 of murex and purpura. Its chemical nature has not been investigated. 



Among the remaining coloring matters found in invertebrates may be men- 

 tioned blue stentorin, actiniochrom, bonellin, poly per ythrin, pentacrinin, antedonin, 

 crustaceorubin, janthinin, and chlorophyll. 



Sebum when freshly secreted is an oily semi-fluid mass which solidifies 

 on the upper surface of the skin, forming a greasy coating. ROHMAXX 



1 Journ. of Physiol., 31. 



2 Vergleichende physiol. Studien, Abth. 5, and (2. Reihe) Abth. 1, 151, Abth. 2, 1, 

 and Abth. 3, 128. 



3 Wurm, cited from Maly's Jahresber., 1; Halliburton, Journ. of Physiol., 6; Merej- 

 kowski, Compt. rend., 93; MacMunn, Proc. Roy. Soc., 1883, and Journ. of Phyisol., 7. 



4 Phil. Trans., 186. ' 



5 Pfliiger's Arch., 98. 



6 Ber. d. deutsch. chem. Gesellsch., 30. 



