Re: I'm told that Peach pits and almonds contain cyanide. Is it harmful to eat

Well, I'm not aware of anyone building up a resistance to cyanide, that's 
for sure.

Cyanide poisoning can happen either acutely or over a longer period of 
time. Over a long period of time, it tends to cause deterioration in the 
visual system, and has been associated with heavy cigarette smoking -- 
cyanide is found in cigarettes, in similar concentrations, I am told, to 
that in the pits and seeds of various fruits, but few people ingest a 
pack's worth of cassava melons...

In any case, cyanide acts by bonding to the same site that oxygen would 
normally bind to in an important player in cellular respiration - 
cytochrome a-a3. Oxygen is the final electron acceptor, and if it is 
blocked by cyanide, than cellular respiration stops. Cyanide also blocks 
the oxygen site in hemoglobin, similarly to carbon monoxide. Both the 
cytochrome and hemoglobin contain a molecule called heme that contains 
iron, and the cyanide binds to the iron in heme in both cases.

There is lots of information available on this topic on the net. One 
particularly good site is eMedicine's electronic textbook.
 
Hope this helps!
:)
Noah Raizman
Francis W. Parker Charter Essential School