METHSEMOGLOBIN.. 247 
the opinion that the colouring matter in methsemoglobin is in the same 
state as in haematin, the iron being, as he thought, in the condition of a 
ferric compound, whilst in oxyhemoglobin and in haemochromogen he 
believed it to exist in a ferrous state, though the grounds for these very 
definite statements are certainly wanting. 
The researches of Hufner on the oxygen of methsemoglobin. 
— I had shown that the action of methsemoglobin, as produced by the action 
of nitrites, cotdd not be attended by a profound alteration in the constitution 
of oxyhemoglobin, seeing that the addition of certain reagents at once caused 
all the effects of the action to disappear, and revealed the continued existence 
of oxidised haemoglobin. Nitrites (for these we should now read all agents 
capable of transforming oxyhemoglobin into methsemoglobin) had, by my 
experiments, been shown to resemble in no way those agents which thrust 
oxygen out of the blood ; on the other hand, I had shown that the action of 
G H K L M N 
Fig. 36. — The photographic spectrum of oxyhemoglobin and methfemoglobin. 
nitrites resulted in the locking up of the oxygen of the blood, so as to render 
it irremovable by carbonic oxide, or by a vacuum. But although I had dis- 
covered that rnethsemoglobin, when treated with reducing agents, at once 
liberates oxyhemoglobin, I had not been able to show that when the latter 
substance is converted into the former the whole of its oxygen is locked up 
without loss, and may be subsequently liberated. This was reserved for 
Hufner. 
When nitric oxide acts upon a solution of methsemoglobin, the brown 
colour is changed to bright red, the spectrum of the red solution being 
identical with that of NO-haemoglobin. Eeflecting on this experiment, Hufner 
thought that perhaps NO possesses the power of becoming oxidised to X0 2 , 
at the expense of the oxygen locked up in methsemoglobin (i.e. oxygen of 
the original oxyhemoglobin which had passed into a more stable combination). 
As such might be the case, it occurred to Hufner to determine the volume 
of N0 2 produced (for this would bear a definite relation to the abstracted 
from methsemoglobin), by causing the nitrous acid (HN0 2 ), which would 
be produced by the action of the water of the blood on NOg, to decompose 
urea, the N liberated being a measure of the oxygen derived from methsemo- 
