For years, Thimerosal has been extremely controversial because there were alternatives to preventing vaccine contamination. And, questions remain about how pharmaceutical companies conduct vaccine research and how the government regulates those companies.

Centuries ago, the shimmering properties of mercury captivated the philosopher Aristotle, who called it "quicksilver" - and the name stuck.

Perhaps the best visual example of what low-levels of mercury can do to the brain is seen in a videotaped experiment by scientists at the University of Calgary.

"Over the next thirty minutes, the neurite membrane underwent rapid degeneration, leaving behind the denuded neurofibrils seen here," the narration on the tape said. "In contrast, other heavy metals added to this concentration - such as aluminum, lead, cadmium and manganese - did not produce this effect."

Starting in the early nineties, government regulators dramatically increased the amount of Thimerosal exposure to babies by adding two new vaccines to the roster of mandatory immunizations children must have before enrolling in school.

The combination of the Hepatitis B vaccine and the HiB vaccine more than doubled the amount of mercury children like Jac Counter received before the age of two.

Jack's parents say today, at age five, he has been diagnosed as having "mercury-induced autism".

"If you take a ten-pound baby in, and it gets four shots on that one day, which is a common practice - that's equivalent to giving a 100-pound person forty shots in one day," said mercury expert Dr. Boyd Haley.

Haley has testified before Congress and the Pentagon as one of the nation's leading experts on Thimerosal and mercury poisoning. The research he's done at the University of Kentucky leads him to believe that some children are genetically predisposed to storing mercury in their brains.

It's the cummulative effect of the mercury which Haley and other scientists say leads to neurological disorders, including autism.

However, members of the government's vaccine committees, like Dr. Jane Siegel, insist the proof isn't there.

Under pressure from the American Academy of Pediatrics, these government committees ordered pharmaceutical companies to stop putting Thimerosal in vaccines by March 2001.

"The topic was researched, it was reviewed, (with) no data to prove a causitive role," Siegel said. "Nevertheless, a call for Thimerosal removal was made. Within two months of the publication of that statement, the Hepatitis B vaccine for infants was free of Thimerosal. Within 18 months, there was on the market all Thimerosal-free vaccine.

"I think this is an incredible achievement."

But did the government really move fast enough to protect America's children? After all, Thimerosal had been used in vaccines since the 1930s.

Documents obtained in a lawsuit show that the government began asking questions about the compound's saftey in 1972. Eli Lilly, which holds the patent on Thimerosal, assured the FDA in a report that "a series of 22 human subjects" were injected with a one-percent solution "without ill effect".

Attorney Andy Waters said what the pharmaceutical giant concealed from the government is that the tests were conducted in 1929 by a young researcher named K.C. Smithburn - on patients dying of mennigitis.

"It's apparent that Lilly didn't want to do the study themselves because it's apparent that there were enormous ethical problems with injecting people - even people dying of meningitis - with mercury," Waters said. "What Smithburn did was wrong, because he agreed to do the study for Lilly, and not only did he agree to do it, but he agreed to give them results that he knew were flawed.

"They knew, and he knew, (the results) were going to be published as the truth."

The FDA questioned Thimerosal's safety again in 1982 - this time, noting that it was "not safe for 'over-the-counter' topical use because of its potential for cell damage". Despite that evidence, however, the government regulatory committees did nothing to question its use in childhood vaccines.

Meanwhile, measures were taken to remove the compound from pet innoculations. More internal company documents and memos show that Eli Lilly began revising its claims about Thimerosal starting in the 1960s, changing package inserts from stating "non-toxic" to "non-irritating to body to issue".

Then, in November 1973, the company's legal division suggested adding the statement: "Do not use when aluminum may come in contact with treated skin". Aluminum is a compound added to many vaccines as a catalyst. But even with this warning, the government committees did nothing.

Haley said any good biochemist knows that Thimerosal and aluminum react dangerously when combined together.

He showed News 8 the results of his experiments on human brain neurons.

"If we add this level of aluminum that we see very little toxicity with to this level of Thimerosal, we get this bottom line ... indicating that we have dramatically enhanced the toxicity, where within 24 hours essentially all of the neurons are dead," Haley said.

Officials at Eli Lilly declined to interview with News 8. However, they did send an e-mail, which said in part that the company's "primary concern is for patient safety". The e-mail also stated that "Lilly discontinued its sale or use of (Thimerosal) about ten years ago".

However, that did not stop other pharmaceutical companies from taking over the production of the vaccine preservative.

In December 1999, shortly before Eli Lilly quit producing thimerosal, the company changed its packaging insert again. This time, Lilly warned that Thimerosal was "toxic". Additionally, it stated that effects of exposure may include "fetal changes, decreased offspring survival, and lung tissue changes".

However, the government's vaccine committee continues to insist that Thimerosal has never been dangerous to American children.

So, the 1999 Eli Lilly package insert was shown to Dr. Jane Siegel for her reaction:

"I cannot comment on this unless I have clarification," Siegel said. "You will have to interview the public. I don't know - I just know that if you show me this piece of paper I cannot make a comment on this - I find it uninterpretable."

Haley said the government should have taken action.

"There should have been an immediate recall of the vaccine," Haley said. "We would do that with an automobile if it had a bad brake system. If we just suspected it had a bad brake system, they would do that. The government has no problems - they'd do it immediately."

The congressional hearing on the use of Thimerosal in vaccines begins in June. While production of the preservative was stopped a year ago, as Dr. Haley pointed out, existing doses were not recalled.

Now, it needs to be re-stated that the easiest solution for parents who are concerned about upcoming immunizations is to simply ask your doctor in advance for Thimerosal-free vaccines.