1875.]} COLOURING OF BIRDS’ EGGS. 363 
probable that there is some important chemical or physical relation 
between the two compounds. 
RELATIONS OF OoRHODEINE. 
It would be difficult to find more striking examples of such a con- 
nexion than oorhodeine and the product of the decomposition of the 
red colouring-matter of blood by strong sulphuric acid, discovered 
and described by Thudicum*. When in a nearly neutral state, dis- 
solved in alcohol, it gives a spectrum of exactly the same character as 
that of oorhodeine in the same physical condition ; and on adding 
a small quantity of a strong acid to both they are both changed 
in the same manner, and give new spectra which are also of ex- 
actly the same character. The spectra of their neutral modifications 
and also those of the very acid solutions have most remarkable and 
unusual peculiarities, quite unlike those of any other substances; and 
therefore one cannot, I think, attribute the resemblance to mere acci- 
dent. The agreement is so close that a superficial observer might 
easily be led to conclude that they were absolutely identical, and that 
oorhodeine was merely Thudicum’s cruentine ; but when the spectra 
‘are compared together side by side with a suitable instrument, it may 
be seen that although the number, relative intensity, and relative 
position of the bands, both in a neutral and acid condition, are ex- 
actly the same, the position of the band is not the same. The 
difference between the spectra is exactly like what is so often seen 
on comparing together the spectra of the same substance dissolved in 
different liquids ; but this explanation will not apply in this case, 
because I find that the position of the bands in cruentine does no¢ vary 
with the nature of the solvent, and the difference between its spectra 
and those of oorhodeine occurs when they are both dissolved in the 
same solvent. In order to show the nature of the relation of the 
spectra, I subjoin the following tables, giving the position of the 
centres of the absorption-bands in millionths of a millimetre of 
wave-length. 
Table 1.— Dissolved in nearly neutral alcohol. 
Oorhodeine ...... .. 630 602 578 539 504 
Cruentine .......... 623 596 572 534 500 
Difference ...... Z 6 6 5 4 
Table 2.— Dissolved in Alcohol with strong Acid. 
Oorhodeine........ 604 580 557 
Cruentine ........ 598 574 552 
Difference .... 6 6 5 
Though I feel much tempted to enter further into the purely 
physical part of the question, it will, I think, be better to confine 
myself to what bears more directly on zoological facts. Following 
* Tenth Report of the Medical Officer of the Privy Council, p. 227. 
