NATURAL COLOURS 441 



chlorophyll in the form of closed chains constituted in the same 

 manner as in the compound known to the chemist as pyrrol : 



CH-CH 



II II 

 CH CH 



NH 



In the derivatives of chlorophyll three or four of these hydro- 

 gen atoms are replaced by methyl, CH 3 or ethyl, C 2 H 5 . 



One of the most interesting facts in connection with this 

 enquiry is the discovery that hsemoglobin, the red colouring 

 matter of blood, yields by chemical decomposition compounds 

 having the same fundamental structure. 



There is thus a near relationship between hsemoglobin and 

 chlorophyll, with one important difference. It has already been 

 mentioned that chlorophyll contains magnesium attached to 

 the nitrogen atoms. Hsemoglobin contains iron in a similar 

 position. The presence of small quantities of a metal as an 

 essential constituent of these colouring matters is a point of 

 considerable interest, and though of much smaller importance 

 a very curious instance is found in the wing feathers of certain 

 birds which contain not iron but copper. The red colour ex- 

 hibited by a number of African birds, called Turacos or Plan- 

 tain-eaters, was examined by the late Sir Arthur Church in 1869, 

 and found to be due to a pigment which he called turacine, 

 which contained some 8 per cent of copper bound up with a 

 nitrogenous structure. 



It appears that turacine is actually a cupriferous derivative of 

 hsematoporphyrin which may be regarded as essentially the 

 colouring matter of blood deprived of its iron. How the birds 

 acquire the copper found in their feathers is not clear, but the 

 same remark would apply to the minute quantity of other 

 elements found in the tissues of animals and plants, the fluorine, 

 for instance, found in the bones and teeth. The papers relating 

 to turacin make no mention of the blood of the birds in whose 

 feathers this red colouring matter is found; presumably the 

 blood contains only iron as in all other cases. 



The only question which appears open to doubt is whether 

 the chlorophylls obtained from different plants are absolutely 

 identical, and whether the chlorophyll obtained from any one 



