208 HAEMOGLOBIN. 



Other reagents which bring about an instant decomposition of 

 oxyhsemoglobin, 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 oxyhasino- 

 globin as they do solutions containing albuminous bodies. 



When subjected to the action of heat, solutions of oxyhsemoglobin 

 coagulate like solutions of the native albumins; but, doubtless, before 

 the temperature of coagulation (64 to 68'5 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 oxyhaemoglobin 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 of oxyhsemoglobin has been replaced by that of alkaline hsematin. 



THE ABSORPTION OF LIGHT BY OXYH^MOGLOBIN. 



(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 Tegion which inter- 

 venes between the lines of Frauenhofer, D and E. 



This discovery at once enabled Hoppe to affirm that haematin, 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 hemoglobin, 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 lie 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 hsematin 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." 8 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 Blutkrystalle," S. 61. 



2 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 Verhalten des Blutfarbstoffes ini Spectrum des 

 Sonnenlichtes," Virchow's Arcliiv, 1862, Bd. xxiii. S. 446-449. 



3 Proc. Roy. Soc. London, 1864, vol. xiii. p. 357. 



