18G4?.] Rediictionand Oxidation of the Colouring Matterof the Blood. 355 



XVIII. " On the Reduction and Oxidation of the Colouring Matter of 

 the Blood." By G. G. Stokes, M.A., Sec. R.S., Lucasian Pro- 

 fessor of Mathematics in the University of Cam bridge. Received 

 June 16, 1864. 



1. Some time ago my attention was called to a paper by Professor 

 Hoppe *, ill which he has pointed out the remarkable spectrum produced 

 by the absorption of light by a very dilute solution of blood, and applied 

 the observation to elucidate the chemical nature of the colouring matter. 

 I had no sooner looked at the spectrum, than the extreme sharpness and 

 beauty of the absorption-bands of blood excited a lively interest in my 

 mind, and I proceeded to try the effect of various reagents. The observa- 

 tion is perfectly simple, since nothing more is required than to place the 

 solution to be tried, which may be contained in a test-tube, behind a slit, 

 and view it through a prism applied to the eye. In this way it is easy to 

 verify Hoppe' s statement, that the colouring matter (as may be presumed 

 at least from the retention of its peculiar spectrum) is unaffected by alkaline 

 carbonates and caustic ammonia, but is almost immediately decomposed 

 by acids, and also, but more slowly, by caustic fixed alkalies, the coloured 

 product of decomposition being the hjjematin of Lecanu, which is easily 

 identified by its peculiar spectra. But it seemed to me to be a point of 

 special interest to inquire whether we could imitate the change of colour 

 of arterial into that of venous blood, on the supposition that it arises from 

 reduction. 



2. In my experiments I generally employed the blood of sheep or oxen 

 obtained from a butcher ; but Hoppe has shown that the blood of animals 

 in general exhibits just the same bands. To obtain the colouring matter 

 in true solution, and at the same time to get rid of a part of the associated 

 matters, I generally allowed the blood to coagulate, cut tlie clot small, 

 rinsed it well, and extracted it with water. This, however, is not essential, 

 and blood merely diluted with a large quantity of water may be used ; but 

 in what follows it is to be understood that the watery extract is used unless 

 the contrary be stated. 



3. Since the colouring matter is changed by acids, we must employ re- 

 ducing agents which are compatible with an alkaline solution. If to a 

 solution of protosulphate of iron enough tartaric acid be added to prevent 

 precipitation by alkalies, and a small quantity of the solution, previously 

 rendered alkaline by either ammonia or carbonate of soda, be added to a 

 solution of blood, the colour is almost instantly changed to a much more 

 purple red as seen in small thicknesses, and a much darker red than before 

 as seen in greater thickness. The change of colour, which recalls the dif- 

 ference between arterial and venous blood, is striking enough, but the 

 change in the absorption spectrum is far more decisive. The two highly 



* Virchow's Archiv, vol. xxiii. p, 44G (13G2). 

 VOL. XIII. 2 D 



