Ill 
of Edinburgh , Session 1866 - 67 . 
arrangements being employed as were used by Hadow in his 
experiments on the constitution of nitro-prussides ; instead, how- 
ever, of generating the nitric oxide by the action of nitric oxide on 
copper, the gas was obtained by boiling a solution of ferric sulphate, 
which had been saturated with NO, in a stream of carbonic acid. 
After the action of nitric oxide had gone on for some seconds, the 
line in the red made its appearance, and the two haemoglobin 
bands became very indistinct, whilst the colour of the blood became 
brown ; the same changes were thus induced as were found to 
occur when nitrites act upon blood. On the addition of ammonia 
the band in the red disappeared, and the spectrum was marked by 
the band in the orange, to which allusion has already been made. 
Although this observation appeared to point to nitric oxide as 
the agent in effecting the change, it was perfectly possible that, 
in reality, it was due to nitrous acid, for it appeared likely that 
this acid might be formed in the blood by the nitric oxide seizing 
that portion of the oxygen of the blood-colouring matter, which is 
capable of removal by reducing agents, or capable of expulsion by 
carbonic oxide. It would indeed appear from my experiments that 
nitrous acid is produced in the reaction, as when by means of a 
long funnel a mixture of potassic iodide, starch, and acetic acid is 
conducted to the bottom of a blood solution, and through which 
nitric oxide is passing, a blue colour is produced. 
In order to separate, if possible, the substance formed under the 
influence of NO in a crystalline form, the blood of a dog was 
allowed to coagulate, and after complete separation of the serum 
the clot was squeezed in linen. The red fluid thus expressed 
was mixed with one-and-a-half times its volume of water, and then 
solution of nitrite of sodium added, until the characteristic spectrum 
was obtained. The fluid was then mixed with one-fourth of its 
volume of 86 per cent, alcohol, when it became filled with micro- 
scopic needles and prisms identical with those of 0 - haemoglobin. 
They merely differed from the latter in having a dirty brown 
colour. They were collected on filter paper, washed with ice-cold 
water, pressed, and afterwards mixed with a considerable quantity 
of water. They did not, however, entirely redissolve, a small 
quantity of a white albuminoid substance remaining undissolved. 
The solution of the crystals presented the same spectrum as the 
blood from which they had been precipitated. 
