2o8 HAEMOGLOBIN. 
Other reagents which bring about an instant decomposition of 
oxyhemoglobin, and, consequently,, instantly set free the albuminous 
matter, exhibit also, as might have been anticipated, the characteristic 
albumin reactions, i.e. behave towards a solution of haemoglobin as if 
it were a solution of a native albumin. This remark applies to acetic 
acid and potassium ferrocyanide, to mercuric nitrate, to the concentrated 
mineral acids — reagents, all of which precipitate a solution of oxyhemo- 
globin as they do solutions containing albuminous bodies. 
When subjected to the action of heat, solutions of oxyhemoglobin 
coagulate like solutions of the native albumins ; but, doubtless, before 
the temperature of coagulation (64° to 68 0- 5 C.) is reached, the complex 
haemoglobin molecule has already been decomposed — a supposition 
which is suggested by the following observation : l — If to an aqueous 
solution of crystallised oxyhemoglobin of the dog a small quantity 
of sodium carbonate be added, on applying heat no coagulation occurs, 
even though the temperature be raised to 100° C. When, however, the 
temperature reaches 54° C, the colour of the solution instantly changes to 
deep brown, and spectroscopic examination indicates that the spectrum 
of oxyhemoglobin has been replaced by that of alkaline haematin. 
The Absorption of Light by Oxyhemoglobin. 
(a) The visible spectrum.— Historical notes.— The researches of 
Brewster and Herschel had shown that absorption-bands occur in the 
spectrum of light which has been passed through certain coloured gases, 
vapours, and coloured solutions, and the so-called absorption spectra of indigo 
and chlorophyll had been described before the time when Hoppe 2 made the 
discovery of the beautiful absorption spectrum of blood, distinguished by 
two very characteristic absorption-bands, situated in the region which inter- 
venes between the lines of Frauenhofer, D and E. 
This discovery at once enabled Hoppe to affirm that haeniatin, which had 
up to that time been generally looked upon as the true blood-colouring matter, 
does not exist as such in the blood corpuscles, but that it is a product of the 
decomposition of the colouring matter ; that the latter, to which he afterwards 
gave the name of haemoglobin, and which he recognised as forming the so-called 
blood crystals described by Kunde, Lehmann, and Funke, is the cause of the 
absorption-bands which he had discovered in the spectrum of diluted blood, 
and that this colouring matter, under the influence of heat, acids, and various 
other chemical agents, splits up into haeniatin and an albuminous substance or 
substances. 
There can be no question that, although Hoppe, in a certain measure, 
appreciated the immense value of the knowledge which he had gained by his 
study of the optical properties of the blood, the full light which it was 
destined to shed on the function of the blood- colouring matter was only 
recognised when Professor Stokes, two years later, published his paper " On 
the Reduction and Oxidation of the Colouring Matter of the Blood." 3 The 
new facts acquired by the combination of chemical and optical methods in 
this research, and which at once shed a flood of light on phenomena which 
had until then been shrouded in darkness, enlisted as workers in this field 
1 Preyer, "Die BlutkrystaUe," 8. 61. 
- Hoppe only assumed the name of Hoppe-Seyler in 1864. The paper containing 
his first observations on the spectrum of the blood bore the following title : — Professor 
Hoppe in Tubingen, "Ueber das Verbal ten des Blutfarbstoffes im Spectrum des 
Sonnenlichtes," Virchow's Archiv, 1S62, Bd. xxiii. S. 446-449. 
3 Proc. Roy. Soc. London, 1864, vol. xiii. p. 357. 
