//. EMOGLOBIN {REDUCED HEMOGLOBIN). 229 
haemoglobin (reduced haemoglobin). 
Synonym, "Purple Cruorin." 
Historical note. —Fully two years had passed since the date of Hoppe's 
publication (1862) of his observations on the spectrum of blood, before it was 
slmwn that the oxygen which enters into combination with haemoglobin has 
a fundamental influence on its spectrum. It was on the 16th of June 1864 
that Professor Stokes * communicated to the Royal Society the interesting 
observation that when diluted blood is treated with certain reducing agents, 
the colour of the liquid and its spectrum undergo remarkable changes ; the 
former loses its bright red appearance, becoming darker in tint, whilst the 
absorption-bands a and ft are replaced by a single band which we may 
designate the band y, which appears less deeply shaded and with less defined 
edges, and which extends from D nearly to E. If, now, the solution which 
exhibits this spectrum be shaken with air or oxygen, the single band at 
once gives place to the two original bands, whilst the liquid reacquires 
more or less of its primitive florid-red colour. The process of reduction 
and oxidation may be repeated many times in succession. 
From his experiments, Stokes concluded that "the colouring matter of blood, 
like indigo, is capable of existing in two states of oxidation, distinguishable by a 
difference of colour and a fundamental difference in the action on the spectrum. 
It man be made to joass from the more to the less oxidised state by the action of 
suitable reducing agents, and recovers its oxygen by absorption from the air." - 
The researches of Magnus, Lothar Meyer, and Claude Bernard had shown 
that the blood holds in solution an amount of oxygen greatly in excess of that 
which could exist in a state of simple solution, but that this oxygen exists in a 
condition which permits of its being extracted from the blood by boiling in a 
Toricellian vacuum, as well as by the action of carbonic oxide. Hoppe-Seyler, 
having succeeded in crystallising oxyhemoglobin, and, by means of its optical 
properties, having identified it with the colouring matter as it exists in the living 
blood, was able to show that a solution of crystallised oxyhemoglobin behaves 
towards red\;cing solutions in the same manner as diluted blood; that, like blood, 
it yields oxygen when boiled in vacuo, and that the blood-colouring matter thus 
deprived in vacuo of its loosely combined or respiratory oxygen manifests the 
absorption-band which had been described by Stokes as the result of reduction. 
The further steps in the growth of our knowledge of reduced haemoglobin 
will be more conveniently referred to in discussing the chief facts with which 
we are acquainted relative to this remarkable body. 
Methods of effecting the reduction of oxyhsemoglobin to reduced 
haemoglobin. — In nearly all experiments 011 the reduction of oxyluemo- 
globin, diluted blood may be substituted for a solution of the pure blood- 
colouring matter, it having been shown by the spectrophotometric and 
chemical researches of Hiifner that, both in respect of their power of 
absorbing light and of the influence of reducing agencies upon them, the 
two solutions possess identical properties. Instead, however, of employ- 
ing pure distilled water as a diluent, it is advisable to use, according to 
Htifner's plan, a 01 per cent, solution of sodium hydrate. A diluted 
solution of blood prepared in this way is free from all turbidity, and 
therefore more transparent than a pure aqueous solution, and undergoes 
putrefactive alterations more slowly. 
1 "On the Reduction and Oxidation of the Colouring Matter of the Blood," Proc. Roy. 
Soc. London, 1864, vol. xiii. pp. 353-364 ; London, Edinburgh, and Dublin Phil. Mag., 
London, 1864, vol. xxviii. pp. 391-400. 
2 Stokes, op. cit., p. 357, par. 8. 
