U Professor A. H. Church Feb. 17, 



WEEKLY EVENING MEETING, 

 Friday, February 17, 1893. 



William Huggins, Esq. D.C.L. LL.D. F.R.S. Vice-President, 

 in the Chair. 



Professor A. H. Church, M.A. F.R.S. M.B.I. 



Turacin, a remarkable Animal Pigment containing Copper. 



The study of natural colouring matters is at once peculiarly 

 fascinating and peculiarly difficult. The nature of the colouring 

 matters in animals and plants, and even in some minerals (ruby, 

 sapphire, emerald and amethyst, for example) is still, in the majority 

 of cases, not completely fathomed. 



Animal pigments are generally less easily extracted and are more 

 complex than those of plants. They appear invariably to contain 

 nitrogen — an observation in accord with the comparative richness in 

 that element of animal cells and their contents. Then, too, much of 

 the coloration of animals, being due to microscopic structure, and 

 therefore having a mechanical and not a pigmentary origin, differs 

 essentially from the coloration of plants. Those animal colours 

 which are primarily due to structure do, however, involve the 

 presence of a dark pigment — brown or black — which acts at once as a 

 foil and as an absorbent of those incident rays which are not reflected. 



Many spectroscopic examinations of animal pigments have been 

 made. Except in the case of blood- and bile-pigments, very few have 

 been submitted to exhaustive chemical study. Spectral analysis, 

 when uncontrolled by chemical, and when the influence of the solvent 

 employed is not taken into account, is very likely to mislead the 

 investigator. And, unfortunately, the non-crystalline character of 

 many animal pigments, and the difficulty of purifying them by 

 means of the formation of salts and of separations by the use of 

 appropriate solvents, oppose serious obstacles to elucidation. Of 

 blood-red or haemoglobin it cannot be said that we know the 

 centesimal composition, much less the molecular weight. Even of 

 haamatin the empirical formula has not yet been firmly estab- 

 lished. The group of black and brown pigments to which the 

 various melanins belong still awaits adequate investigation. We 

 know they contain nitrogen (8J- to 13 per cent.), and sometimes iron, 

 but the analytical results do not warrant the suggestion of empirical 

 formulae for them. The more nearly they appear to approach 

 purity the freer the majority of them seem from any fixed con- 

 stituent such as iron or other metal. It is to be regretted that 

 Dr. Krukenberg, to whom we are indebted for much valuable work 



