PRUSSIC ACID ON THE ANIMAL ECONOMY. 2a 
viduals who were in full health, and in all these I found the 
same kind of particles. The majority of these particles, as 
well as several obtained from the experiments narrated, were 
tested with oxalic acid, which readily decolourised and dis- 
solved them away. 
The evidence at this pomt of my observations assumed a 
very contradictory character; and if I had not been at the 
time in possession of other facts which supported me in my 
views, I should have been brought to an unsatisfactory stand- 
still. 
12. In the course of my experiments I took occasion to 
examine the prussic acid itself as to its purity, and the fol- 
lowing observations will tend to clear up the evidence. 
Prussic acid, like some other powerful and effective agents in 
the hands of the medical man, possesses the property of ra- 
pidly undergoing a chemical change and of losing its powers 
as a medicine; this lability to change has been referred to 
the action of light, and also been noticed to occur more fre- 
quently the greater the degree of its concentration. Hence, 
it is now usually kept covered up from the action of light, 
and preserved in a certain state of dilution, and also appears 
to be more permanent when prepared after a certain manner. 
13. If the ordinary prussic acid of Scheele be examined 
under the microscope under a power of 200 diameters, the 
acid, if pure, will present nothing worthy of remark; but 
occasionally specimens will be met with which contain bright 
blue particles, consisting, as I suppose, of Prussian blue, and 
also a number of starchy looking bodies, which actually turn 
purple with iodine. Or, sepposing the acid to have been pure, 
these changes will be found to take place in it, if the bottle 
is repeatedly opened and portions taken out ever so carefully, 
by dipping a glass rod into the fluid; at least such is my 
experience. 
14, These remarkable changes appear to me to be due to 
the renewed access of air, and minute particles of dust get- 
ting in, and to the possible electric state of the glass rod with 
which I have been in the habit of dipping out the acid, having 
always previously carefully wiped it. 
If, after the occurrence of these accidents, extended over a 
period of many days, the bottle be shaken, and a drop placed 
on a slide and examined with a microscope, bright blue par- 
ticles will be seen associated with a number of starchy looking 
bodies, which polarize feebly and turn purple with iodine, 
like vegetable starch. 
15. On taking a drop of prussic acid, free from such con- 
tamination, as, for example, by using some which has not 
