1893.] on Turacin, a remarkable Animal Pigment. 49 



of hreniatoporphyrin. But, unlike this derivative of h*eroatiu, it seems 

 to retain some of its metallic constituent. The analogy between the 

 two bodies cannot be very close, for if they were so nearly related as 

 might be argued from the spectral observations, hjematin ought to 

 contain not more but less metal than is found to be present therein. 



The percentage composition of turacin is probably — Carbon 53 ■ 69, 

 hydrogen 4 ■ 6, copper 7*01, nitrogen 6*96, and oxygen 27 ■ 74. These 

 numbers correspond pretty nearly to the empirical formula, C 82 H 81 

 Cu 2 N 9 32 . But I lay no stress upon this expression. 



I have before said that copper is very widely distributed in the 

 Animal Kingdom. Dr. Giunti, of Naples, largely extended (1881) our 

 knowledge on this point. I can hardly doubt that this metal will be 

 found in traces in all animals. But besides turacin only one organic 

 copper compound has been as yet recognised in animals. This is a 

 respiratory, and not a mere decorative, pigment like turacin. Leon 

 Fredericq discovered this substance, called haemocyanin. It has been 

 observed in several genera of Crustacea, Arachnida, Gastropoda and 

 Cephalopoda. I do not think it has ever been obtained in a state of 

 purity, and I cannot accept for it the fantastic formula — C 867 H 1369 Cu 

 S 4 258 — which has recently been assigned to it. On the other hand, 

 I do not sympathise with the doubts as to its nature which F. Heim 

 has recently formulated in the Comptes Bendus. 



It is noteworthy, in connection with the periodic law, that all the 

 essential elements of animal and vegetable organic compounds have 

 rather low atomic weights, iron, manganese and copper representing 

 the superior limit. Perhaps natural organic compounds containing 

 manganese will some day be isolated, but at present such bodies are 

 limited to a few containing iron, and to two, haeinocyanin and turacin, 

 of which copper forms an essential part. 



If I have not yet unravelled the whole mystery of the occurrence 

 and properties of this strange pigment, it must be remembered that it 

 is very rare and costly, and withal difficult to prepare in a state of 

 assured purity. It belongs, moreover, to a class of bodies which my 

 late master, Dr. A. W. von Hofmann, quaintly designated as " dirts" 

 (a magnificent dirt truly !)— substances which refuse to crystallize 

 and cannot be distilled. I have experienced likewise, during the 

 course of this investigation, frequent reminders of another definition 

 propounded by the same great chemist, when he described organic 

 research as " a more or less circuitous route to the sink ! " 



I am very glad to have had the opportunity of sharing with an 

 audience in this Institution the few glimpses I have caught from time 

 to time during the progress of a tedious and still incomplete research 

 into the nature of a pigment which presents physiological and chemical 

 problems of high if not of unique interest. 



Let my last word be a word of thanks. I am indebted to several 

 friends for aid in this investigation, and particularly to Dr. MacMunn, 

 of Wolverhampton, the recognised expert in the spectroscopy of animal 

 pigments. [A. H. C] 



Vol. XIV. (No. 87.) E 



