23S HAEMOGLOBIN. 
showed — (1) that the absorption of oxygen and carbonic oxide by blood does 
not proceed according to Dalton and Henry's law — a proof, amongst many 
others, that these gases are chemically combined with some constituent of 
the blood and not held in a state of simple solution ; (2) that blood which 
has been deprived of its gases by boiling in vacuo, combines with the same 
volume of carbonic oxide as of oxygen — in other words, that when carbonic 
oxide replaces the oxygen of the blood, one molecule of the former takes the 
place of one molecule of the latter (i.e. CO replaces 0. 2 ). Lothar Meyer 
further showed that hsematin could not be the body with which 2 and CO 
entered into combination, and expressed the surmise that it might prove 
to be the same as constituted the red blood crystals described by Lehmann. 1 
The truth of the surmise was soon proved beyond the possibility of doubt, 
it being shown that the 0. 2 - and CO-compounds of the blood-colouring matter 
are isomorphous, that they are characterised by a similarity in their power of 
absorbing light, but that the CO-compound is distinguished by not being 
decomposed by reducing agents (Hoppe-Seylef). 
Hermann 2 subsequently showed that just as CO possesses the power 
of displacing the oxygen of oxyhemoglobin, nitric oxide (NO) in its 
turn is capable of displacing CO, one molecule of the former replacing 
one molecule of the latter, the NO-compound being, like the CO-com- 
pound, absolutely irreducible. 
The three compounds of haemoglobin were shown to be isomorphous, 
to be characterised by a highly florid colour, only slightly differing in 
tint one from the other ; their visible spectrum was found to be distin- 
guished by two absorption-bands between D and E, at first sight appear- 
ing identical in the three cases, though careful measurement revealed a 
very slight shifting of the bands towards the more refrangible end of the 
spectrum in the case of the CO-compound. 
They were all three found to be free from pleochromatism — 
a character in which they differ strikingly from reduced haemo- 
globin. Whilst the CO - compound is much more stable than the 
2 -compound, the NO-compound is again more stable than the CO- 
compound. 
It was at first believed that the CO-compound, unlike oxyhaenio- 
o-lobin, could not be dissociated. I was the first to show that by the 
long-continued passage of neutral gases through solutions of CO-haemo- 
globin, the CO is gradually driven out, and reduced haemoglobin is 
obtained. 3 Donders, 4 to whom the discovery of the fact is always 
ascribed, drew attention to it in a highly interesting theoretical paper. 
Zuntz 5 immediately afterwards showed, in contradiction of Nawrocki, 6 
that blood saturated with carbonic oxide, when boiled in vacuo, gives up 
its carbonic oxide and that it manifests the absorption-band of reduced 
1 " Consideranti enim qure his in rebus din versatus Lehmann de rubris illis sanguinis 
crystallis nuper publicavit, plus quam verisimile videbitur, hac cum substantia et oxygenium 
et oxydum carbonicum conjunctionem chymicam posse mire"; Lothar Meyer, "De 
sanguine oxvdo carbonico infecto," p. 12. 
2"TJeber die Wirkungen des Stickstoffoxydgases auf das Blut," Arch. f. Physiol., 
Leipzig, 1865, S. 469. 
3 A. Gamgee, "On Poisoning by Carbonic Oxide Gas, and by Charcoal Fumes," 
Journ. Anat. and Physiol., London, 1867, vol. i. pp. 339-346. 
4 Donders, " Der Cbemismus der Athraung, ein Dissociations-process," Arch. f. d. ges. 
Physiol., Bonn, 1872, Bd. v. S. 20-26. 
5 "1st Kohlenoxydhamoglobin eine feste Verbindung ? " Arch. f. d. ges. Physiol., 
Bonn, 1872, Bd. v. S. 584-588. 
6 "De Claudii Bemardi methodo oxygenii copiam in sanguine determinandi," Inaug. 
Diss., Vratislavicc, 1863. 
