//. EMOCHROMOGEN. 257 
When subjected to the action of such reducing agents as tin and 
hydrochloric arid, haemochromogen gives rise to coloured products, which 
are obviously nearly related to, though not identical with, such bodies as 
the so-called urobilins. 
It was stated that when blood saturated with CO, or a concentrated 
solution of CO-haemoglobin, is treated with a concentrated solution of 
sodium hydrate, a bright red precipitate separates. Jaderholm stated 
that this precipitate consisted of a compound of CO with haematin, and 
could be prepared directly by the action of the gas on a solution of 
reduced haematin; he further asserted that the visible absorption- 
spectrum of the CO-haematin closely resembled that of CO-haemoglobin, 
the bands occupying the same position ; though he described them as 
being less intense in the haematin compound, and as differing from the 
CO-haemoglobin compound in the fact that the two bands « and 3 
exhibit equal intensities. 
By causing an alkaline hydrate to act upon CO-haemoglobin in the 
absence of oxygen (method with double tubes previously described), and 
heating to 100° C, Hoppe-Seyler separated the body which Jader- 
holm had described as CO-haematin, but which appears really to be 
CO-haemochromogen. Like haemochromogen itself, its CO-compound, 
which has been deposited at 100° C, dissolves again when 
the liquid from which it separates cools. The CO-compound of 
haemochromogen is described by Hoppe-Seyler as a crystalline body, 
though none of its physical characters have been subjected to even a 
superficial examination. The visible spectrum of its solution is, accord- 
ing to Hoppe-Seyler, absolutely undistinguishable from that of CO- 
haemoglobin. 
The most interesting and weighty observation made by Hoppe- 
Seyler on this subject w r as, however, that concerning the volume of CO 
which combines with haemochromogen to form its CO-combination. He 
found that the same volume of CO combines with haemochromogen as 
would be required to convert an equivalent weight of reduced haemo- 
globin into the CO-compound. This unquestionably interesting ob- 
servation, taken in connection with the fact that crystals form under 
certain circumstances in solutions which contain CO-haemochromogen 
(there is no absolute proof that the crystals represent this substance), 
led Hoppe-Seyler to form certain hypotheses of extraordinary boldness, 
for which the experimental bases are as yet altogether wanting, but 
which have been accepted with misplaced confidence ; these hypotheses 
he looked upon as legitimate conclusions from his own experiments, and 
formulated as follows : — 
" We are justified in concluding that in crystallised CO-haemoglobin, 
as w r ell as in the colouring matter of the blood corpuscles, there is 
present a particular group of atoms which combines with and retains 
carbonic oxide, which is characterised by the special manner in which it 
absorbs light, and which, after separation from the albuminous residues, 
passes unchanged into CO-haemochromogen. 
" Without possibility of doubt, this group of atoms is identical with 
the one which, in the arterial blood-colouring matter, 1 and in crystallised 
oxyhemoglobin, holds two atoms of oxygen in combination, in the place 
of a molecule of CO. 
" The oxyhemoglobins, the haemoglobins, and the CO-haemoglobins, as 
1 Reference is here made to the hypothetical "arterin." 
VOL. I. — 17 
