Thimerosal is 49.6% mercury.
In solution, Thimerosal rapidly breaks down to ethyl-mercury, a organic form of mercury, and sodium thiosalicylate.
One half milliliter dose of a Thimerosal-containing vaccine hypothetically carries a concentration of mercury at a level of 55 parts per million into the bodies of infants and toddlers, as well as the unborn children still inside their mommy's tummy.
Organic mercury itself is not what causes neurological problems. Neurotoxicity problems arise when the organic form of mercury compound decomposes into to the inorganic mercuric mercury form.
Ethyl-mercury, the organic form of vaccine mercury, crosses the blood-brain barrier where it decomposes into inorganic, mercuric mercury.
In terms of ranking mercury compounds by neuro-toxicity, ethyl-mercury is at the top of the list.
It is noted in the literature that as ethyl-mercury was found to be decomposing to inorganic in the brains of children this was not part of the detoxification process.
Methyl-mercury, the organic form of tuna mercury, also crosses the blood-brain barrier, but it does not appear to decompose into the neurologically damaging inorganic, mercuric mercury as much as the organic form of vaccine mercury does.
American infants and toddlers do not come with full chem suits as the US Environmental Protection Agency suggests lab workers don prior to laboratory Thimerosal exposure, and they do not typically munch tuna sandwiches prior to an age of having teeth to munch them with.
Also as Dan Olmsted indirectly points out, doctors do not use syringes to directly inject tuna salad into the bodies of America's infants and toddlers, but they do inject ethyl-mercury laced vaccines into them still.
Incidentally, the 2005 study mentioned by Olmsted, Burbacher et al (2005), was seized upon by both sides of the Autism-Mercury debate.
One side saw the greater levels of inorganic mercury in the vaccine mercury brain tissue specimens.
The other side took the blood results to their mass media outlets prior to the meeting, and then flapped them around in the air at the 2004 Institutes of Medicine Autism-Mercury meeting as if they were Neville Chamberlain waving his "peace in our time" contract with Adolf Hitler claiming "it all gets pooped out". This was very careless to do since either fecal mercury samples of monkey dropping were not taken at all as part of the 2005 study, or they were taken and the authors of the study decided to not publish them.
So whether or not the 2005 study adds up to a hill of beans, at all, relates to accuracy and relevant methodology.
Demonstrating Autism as a result of micro-mecurialism or macro-mecurialism in very small subjects can be affected by whether or not the actual specimens are representative of portions of brains associated with cognitive skills, or tissue results came by scrambling lots and lots of monkey brains in a blender and separating the liquid mercury results from the solid mercury results and calling them organic or inorganic.