xi THE ALBUMINOIDS : SPONGIN, ETC. 573 



gave the substance its name, by Harnack, 1 and by Kossel and 

 Kutscher. 2 The analyses 3 show a low carbon-content; sulphur is 

 present; the dissociation-products are given on p. 73, No. 33. The 

 basic radicals are present in abundance, and so are leucin, glycocoll, 

 and glutaminic acid. Tyrosin is absent. It dissolves at the ordinary 

 temperature only in very concentrated H 2 SO 4 or HC1, more readily in 

 caustic potash and in ammoniated copper oxide, and also in superheated 

 water. 4 The presence of iodine, first observed by Croockewit, is of 

 special interest. Harnack prepared from sponges the iodo-spongin, an 

 abiuretic, iodised dissociation-product (compare p. 234). The support- 

 ing frameworks of the tropical and subtropical horny sponges, which 

 contain in older specimens up to 14 per cent of iodine, according to 

 Hundeshagen 5 do not belong to this group, but to the keratins, as they 

 yield an iodised tyrosin, which ordinary spongin probably does not do. 

 A detailed account is still wanting. 



Conchiolin forms the organic ground matrix of the shells of molluscs. 

 . It was first examined by von Voit, 6 and subsequently by Krukenberg, 7 

 Engel, 8 and especially Wetzel. 9 It is only slightly soluble in acids 

 and in superheated water, but fairly readily in alkalies, at least as long 

 as it is young, for old conchiolin, according to Voit, is much more 

 insoluble. It gives the biuret- and xanthoproteic tests and Millon's 

 reaction. Its dissociation - products are given on p. 73, No. 31. 

 Conchiolin contains in addition 8 '6 6 per cent of its nitrogen in a basic 

 form (Wetzel). A carbohydrate radical and iodine seem to be absent, 

 while sulphur and, according to Voit, also iron are present, but it does 

 not give the lead-sulphide reaction. In the shells of mussels, conchiolin 

 is arranged in definite lamellae, which, notwithstanding their different 

 colours, do not show any considerable difference in their chemical 

 constitution. The eggs of snails [Murex] also contain conchiolin 

 (Engel). 



Cornein forms the framework of corals ; it yields indol, according 



1 E. Harnack, Zeitschr. f. physiol. Chem. 24. 412 (1898). 



2 A. Kossel and F. Kutscher, ibid. 31. 165 (1900). 



3 L. Posselt, Liebig's Annalen, 45. 192 (1843) ; J. H. Croockewit, ibid. 48. 43 

 (1843) ; E. Harnack, Zeitschr. f. physiol. Chem. 24. 412 (1898). 



4 F. C. W. Krukenberg, Zeitschr. f. Biol. 22. 241 (1886). 



5 F. Hundeshagen, Ghent. Zentralbl. 1895, II. p. 570. 



6 C. Voit, 'Physiologie der Perlmuschel,' Zeitschr. f. wissenschaftl. Zool. 10. 470 

 (1860). 



7 F. C. W. Krukenberg, Ber. d. deutsch. chem. Ges. 18. I. 989 (1885) ; Zeitschr. f. 

 Biol. 22. 241 (1886). 



8 W. Engel, Zeitschr. f. Biol. 27. 374 (1890) ; 28. 345 (1891). 



9 G. Wetzel, Zeitschr. f. physiol. Chem. 26. 535 (1899) ; 29. 386 (1900) ; Zentralbl. 

 f. Phys. 13. No. 5 (1899). 



