230 RALPH, ON THE EFFECTS OF 
and the use of a magnifying power of 500 diameters. The 
films of blood examined were remarkable for the great amount 
of black-looking particles which were present. These I am 
inclined to regard either as iron in a peroxidized state, or 
they are dark particles of Prussian blue, and due to the iron 
lately taken by the patient. These dark particles recall the 
appearances seen in the 3rd experiment. The blood on each 
slide was not greater in bulk than the head of a large pin. 
9. In a patient of mine, a child to which I had occasion to 
administer prussic acid (one minim and a half in twelve 
hours), I took blood on four slides, and in three I found 
blue particles. The acid was continued to the same ex- 
tent, and six more slides charged; each showed the blue 
particles in greater abundance, and also some dark blue 
or indigo-coloured films. The bright blue particles which 
I always look for as the most characteristic colour indi- 
cating the action of prussic acid was in this case so de- 
cidedly associated with concretionary masses peculiar to the 
blood, that there could be no possible doubt as to their in- 
ternal origin, and not from any extraneous source. Liquor 
ammoniz and potasse and nitric acid, separately, do not ap- 
pear to act on the blue particles, but the last two do so when 
following each other. 
10. From these observations, I feel satisfied in advancing 
the opinion that prussic acid causes a change in some of the 
constituents of the blood, that it attacks the iron when in 
some particular condition, and, with perhaps the aid of some 
alkaline base, the Prussian blue is formed; that the deep or 
indigo-blue particles may be some mixture of iron and Prus- 
sian blue, or a state of Prussian blue not definitely known to 
us; for this chemical compound is not yet fully understood 
as to its exact composition, and is found to vary both in 
colour and composition in the laboratory of the chemist, and 
may do so also in that of the animal economy. On the other 
hand, I find there is a cyanide of iron known which turns 
blue on exposure to oxygen, and perhaps ultimately these 
blue particles in the blood may be found to belong to this 
cyanogen compound.* 
11. Continuing my observations on the blood as oppor- 
tunity presented, I detected the presence of these blue par- 
ticles in one or two cases in which no prussic acid had been 
given, and I could in no way satisfactorily account for their 
presence. This led me to examine the blood in three indi- 
* ‘Watt's Chemical Dictionary,’ vol. ii, p. 221, “Some of the compounds 
called Prussian blue have the composition of cyanides of iron; they appear 
to be double cyanides.” 
