I know exactly what mercury poisoning is, and what it's symptoms are, thank you very much. I assume you've checked on how much mercury is required to produce these symptoms? [as I have]

you will see many parents doing Chelation therapy, an experimental very expensive procedure

Yes, I will - in many cases without any evidence whatsoever that their children HAVE heavy metal poisoning. Its called "grasping at straws". [P.S.- if the child is already displaying symptoms of autism,it would seem rather a pointless exercise, would it not?]

Now, what is the SOURCE of the "high levels of mercury" in SOME, not all, autistic children, particularly since the amount of mercuric compound once and no longer used in the vaccinations you irrationally condemn is so infinetesimal that it could in no way produce "high levels of mercury" in their blood if thet were vaccinated eavch and every day for a year...