The use of poisons in war,
specifically poison gas, started in the First World War.
But one of the most potent poison gases,
nerve gases ever discovered is the compound called sarin.
This was developed by the Germans in the 1930s,
and taken over by the German military.
In the World War II,
the Germans stockpiled a lot of sarin,
but it was never used.
And most of it was discovered by the Russians,
as they push through into Germany.
All sorts of countries have made and have stockpiled sarin.
And most, quite recently,
we've seen that the United States going to the verge of military action against Syria,
because of the use of sarin in the Syrian Civil War.
One terrible use of sarin was back in 1988,
when the Saddam Hussein's military in Iraq used it against villages up in the Kurdistan,
in the north of the country.
Sarin is a very,
very powerful nerve agent.
It gets into the body,
it stops the nervous system working,
and even with very low doses causes death.
It's not just governments that have made sarin.
This Japanese cult called Aum Shinrikyo also had a go at making sarin.
And they released some in a town called Matsumoto,
in June of 1994, killing seven people.
The following year, they carried out the well-known Tokyo subway attack,
where they released their homemade sarin in the Tokyo subway.
They killed 12 people.
A 1000 people at least went to hospital,
and even today there are still people suffering the ill effects of that attack.
Fortunately, the Aum Shinrikyo chemists weren't very good at their job.
The sarin they produced wasn't very pure,
and it smelled very badly.
If they'd made pure sarin then the death toll would have been much, much higher.
Well, how do these nerve agents work?
They work by interfering with the biochemical mechanism in
which nerve impulses travel from the brain to the muscles.
So, this is a nerve cell,
and it does look like a piece of wire and in
some ways it acts like a piece of wire in transmitting the message.
So, how does a nerve cell actually work in chemical terms?
Well, let's consider a nerve cell in its resting state,
where nothing is going on.
Here's the nerve cell.
Before it is the previous nerve cell,
in front of it is another nerve cell.
And it's this line of nerve cells which will ultimately carry
the impulse from the brain to the muscle.
Well, the resting state those potassium ions inside the cell,
there's sodium ions outside the cell,
and the cell has a slight negative voltage.
At the business end of the cell there's a little molecule sitting there.
This is called the neurotransmitter,
and the job of the neurotransmitter is to jump across the synapse,
to trigger the next nerve cell in the line.
The signal comes down the line,
the neuron becomes excited and passageways in the cell wall open up,
and these passageways are sodium channels.
They will allow sodium to flow into the cell.
So, sodium flows from outside the cell into the cell,
which means that the voltage becomes positive.
So the neuron is excited.
It's now a plus 30 mV,
and the neurotransmitter is released.
Now, this neurotransmitter is a little molecule called acetylcholine.
It's released, it crosses
the synapse and when it gets to the nerve cell on the other side,
it then excites that one,
and the message continues down the line.
So, the nerve cell that we're looking at now has to get back to its original state.
Passageways in the cell wall open,
these are potassium channels and potassium is released.
The final thing is that ion pumps redistribute the sodium and potassium,
so the potassium goes back in the cell,
the sodium comes out,
and we're back where we started,
we're back at the original state.
Now, the neurotransmitter has done its job,
so at some point it either has to go back to where it started or it has to be removed.
And it's removed by being destroyed by a particular enzyme called acetylcholinsterase.
And this whole process takes two milliseconds.
Very remarkable piece of chemistry.
But remarkable piece of chemistry,
what happens when we interfere with it?
Sarin interferes at the neurotransmitter stage.
Suppose, we have excess of the neurotransmitter present. What will happen?
Well, it mean we get continued nerve stimulation.
Even though there is no signal coming down from the line, from the brain,
the nerve is still stimulated,
and that means that the muscles at the end of the nerve are still activating.
This leads to twitching.
It leads to convulsions.
It leads to paralysis and death.
It often starts with blindness,
due to the effect on the eye muscles and the eye nerves.
Now, under what circumstances would we have excess of the neurotransmitter present?
Well, the concentration of the neurotransmitter is
regulated by this enzyme called acetylcholinsterase,
which converts the acetylcholine into inactive choline.
What sarin does is block the action of that enzyme,
so that the excess acetylcholine cannot be destroyed,
and therefore will be present in excess.
