PRUSSIC ACID ON THE ANIMAL ECONOMY. 229 
The object of giving the tincture of iron to a frog, and then 
killmg it by vapour of prussic acid, was to prove that the 
change was due to the presence of iron in the blood, and, if 
so, a superabundance of iron might yield a proportionate in- 
crease in the amount of the blue particles. This did not 
seem to be the case, but will be noticed further on. 
7. The impression left on my mind by these experiments 
was, that the bright blue particles were due to the action of 
prussic acid on the iron in the blood or tissue in some state 
of organic combination, and that Prussian blue had been 
formed. 
The dark-coloured or indigo-blue masses appear to me to 
be a mixture of Prussian blue and perhaps some oxidized 
state of iron unacted on by the prussic acid. The adminis- 
tration of prussic acid in a concentrated state, 7. e. without 
further dilution of the Scheele’s strength (=4 per cent. of 
real acid) appeared to me to be followed by a greater forma- 
tion of the dark blue particles than when given in diluted 
and distant doses. 
The two experiments not subjected to the action of prussic 
acid, Nos. 5 and 8, gave negative evidence in favour of the 
same view. 
The instances quoted of blue-coloured particles occurring 
in the blow-fly without previous action of prussic acid, may 
depend on the cause I have noticed, or on another. This 
roving insect may derive sufficient cyanogen materials from 
the putrescent substances it is in the habit of visiting, or may 
possibly derive them from the flowers it seeks to, which I 
believe it is in the habit of doing, as I have seen pollen-grains 
in abundance about its body while making these observations. 
I would here remark that the frog’s tissues contain pig- 
mentary matters in abundance, and these might be mistaken 
for the dark blue particles I have instanced ; but when these 
bright and dark blue objects have once been seen elsewhere, 
no mistake of the kind need occur, or be charged against the 
experiments. I here specially refer to examinations of the 
nerves of the frog. 
8. For the purpose of further testing the action of prussic 
acid on the blood, I obtained some from a patient in the 
Melbourne Hospital, who was and had been taking this me- 
dicine lately for some days. I felt some objection to this 
case, as the tincture of iron hadebeen freely administered 
prior to the prussic acid, and I thought its action might in- 
terfere with the character of the experiment. 
Four slides were charged; in each of these the peculiar 
blue particles were distinctly seen, but it required much care 
