II THE PIGMENTS OF ORGANISMS 49 



modem chemistry, and have heard of the wonderful 

 discoveries as to the composition of the sun and 

 some of the stars which have followed from the 

 spectroscopic examination of the light emitted by 

 these bodies. Now we have already seen that 

 many of the pigments of plants and animals are 

 extremely fugitive and unstable, many of them also 

 are exceedingly difficult to extract from the tissues. 

 By means of the spectroscope, however, the coloured 

 tissues may often themselves be directly examined, 

 and on account of the readiness with which the 

 operation may be performed, a large number of 

 pigments are known chiefly by their spectra. Now 

 even in the case of the metals, we find an authority 

 like Mr. Crookes saying that " inferences drawn from 

 spectrum analysis per se are liable to grave doubt, 

 unless at every step the spectroscopist goes hand in 

 hand with the chemist." If this be true of radiant 

 matter spectroscopy, where the spectra are capable 

 of extraordinarily accurate study, how much more 

 likely is it to be applicable to the spectrum analysis 

 of pigments, where the methods are as yet clumsy 

 and inadequate ! Thus we find as a matter of 

 practical experience, that it has been found impos- 

 sible in the aniline industry to employ the spectra 

 as a test for affinity. Again, in spite of the 

 common assertion that pigments yielding identical 

 spectra are themselves identical, we find that three 

 distinct pigments — haemoglobin, carmine, and turacin 

 — are described by competent authorities cis giving 

 spectra which are virtually identical. Turacin, a 

 pigment discovered by Professor Church, is of 

 purplish-violet colour, and occurs in the feathers of 



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