1864.] 



of the Colouring Matter of the Blood. 



357 



6. Of course it is necessary to assure oneself that the single band in the 

 green is not due to absorption produced merely by the reagent, as is readily 

 done by direct observation of its spectrum, not to mention that in the 

 region of the previous dark bands, or at least the outer portions of it, the 

 solution is actually more transparent than before, which could not be occa- 

 sioned by an additional absorption. Indeed the absorption due to the 

 reagent itself in its dilferent stages of oxidation, unless it be employed in 

 most unnecessary excess, may almost be regarded as evanescent in com- 

 parison with the absorption due to the colouring matter ; though if the 

 solution be repeatedly put through its changes, the accumulation of the 

 persalt of iron will presently tell on the colour, making it sensibly yellower 

 than at first for small thicknesses of the solution. 



7. That the change which the iron salt produces in the spectrum is due 

 to a simple reduction of the colouring matter, and not to the formation of 

 some compound of the colouring matter with the reagent, is shown by the 

 fact that a variety of reducing agents of very different nature produce just 

 the same effect. If protochloride of tin be substituted for protosulphate 

 of iron in the experiment above described, the same changes take place 

 as with the iron salt. The tin solution has the advantage of being colour- 

 less, and leaving the visible spectrum quite unaffected, both before and 

 after oxidation, and accordingly of not interfering in the slightest degree 

 with the optical examination of the solutions, but permitting them to be 

 seen with exactly their true tints. The action of this reagent, however, 

 takes some little time at ordinary temperatures, though it is very rapid if 

 previously the solution be gently warmed. Hydrosulphate of ammonia 

 again produces the same change, though a small fraction of the colouring 

 matter is liable to undergo some different modification, as is shown by the 

 occurrence of a slender band in the red, variable in its amount of develop- 

 ment, which did not previously exist. In this case, as with the tin salt, the 

 action is somewhat slow, requiring a few minutes unless it be assisted by 

 gentle heat. Other reagents might be mentioned, but these will suffice. 



8. We may infer from the facts above mentioned that the colouring 

 matter of blood, like indigo, is capable of existing in two states of oxida- 

 tion, distinguishable by a difference of colour and a fundamental difference 

 in the action on the spectrum. It may be made to pass from the more to 

 the less oxidized state by the action of suitable reducing agents, and re- 

 covers its oxygen by absorption from the air. 



As the term hcBmatin has been appropriated to a product of decomposi- 

 tion, some other name must be given to the original colouring matter. As 

 it has not been named by Hoppe, I propose to call it cruorine, as suggested 

 to me by Dr. Sharpey ; and in its two states of oxidation it may conveniently 

 be named scarlet cruorine and purple cruorine respectively, though the 

 former is slightly purplish at a certain small thickness, and the latter is of 

 a very red purple colour, becoming red at a moderate increase of thickness. 



9. When the watery extract from blood- clots is left aside in a corked 



2 D 2 



