234 RALPH, ON PRUSSIC ACID. 
appears to me that a large and important field of inquiry has 
been opened to the investigations of the chemist, and among 
the speculations to which these facts may lead there is this 
to consider—that perhaps Prussian blue should rather be 
regarded as a cyanide of iron than a sesquiferro-cyanide ; 
and that iron, perhaps, performs other functions in the blood 
than that connected with oxygen—that of being a vehicle or 
medium for holding carbon and hydrogen together, for their 
more ready distribution to the building up of tissues, and to 
the preserving them in a condition which may be more easy 
of change by reason of their union with the iron. 
22. The fact of the formation of Prussian blue in the 
animal economy from the action of prussic acid should 
suggest the possibility of detecting this poison in cases of 
poisoning, remembering that, while the volatile and easily 
decomposable nature of this agent enables its traces soon to 
fade away from our chemical grasp, those portions of the 
poison which have gone to form Prussian blue in the blood 
may remain for an indefinite périod as evidences of its 
presence. On the other hand, if it be true that in some 
cases prussic acid or some cyanogen compound may be 
formed spontaneously in the body, as has already been 
suggested by others besides myself, so we may have an 
increased difficulty presented to us in a judicial point of view 
in arriving at the conclusion on microscopical evidence alone, 
that anyone has been poisoned by this agent. 
23. Again, with respect to the spontaneous formation of 
Prussian blue in the blood, the suggestion presents itself— 
may not the iron in the blood be the normal antidote to the 
cyanogen so formed; and supposing that iron was not pre- 
sent in a suitable condition or sufficient amount to neutralize 
the cyanogen, then spontaneous poisoning would be the 
result; and may we not, with this view of the process, be 
warranted in endeavouring to ascertain if the occurrence of 
some diseases of the nervous system, as chorea, convulsions, 
&c., may not be due to some deficiency in the blood at the 
time of a suitable condition or amount of iron? And, 
further, the pathologist will have to ascertain more par- 
ticularly what organs are more especially liable to injury 
under the action of prussic acid. 
24. Before concluding this communication it may be 
desirable to direct attention to the fact that some years ago 
the formation of indigo was pointed out as taking place both 
in the tissues of the body and also in the urine. The papers 
on this subject are by Dr. Hassall, and may be consulted in 
the ‘ Transactions of the Royal Society of Great Britain’ for 
1855. 
