Question

Is mercury a poison for humans?

Answer 1

Mercury causes damage to the central nervous system.

Explanation:

Mercury tends to dissolve dendrites and other parts of the nervous system. A small amount of mercury does not necessary have to be harmful, but since our body cannot get rid of it on its own, it will accumulate in our bodies until it reaches dangerous amount.

The mad hatter in "Alice in wonderland" is a literary example of the harmful affects of mercury poisoning. Hatters of that era used mercury to paint images on the popular felt hats. In licking the brushes to get a good point, the hatters ingested mercury.
The mercury caused the hatters to become insane over time.

Mercury poisoning may happen through bioaccumulation along food chain, as recognised in a community living near Japan's Minamata Bay. The disease was first reported as an unknown epidemic in 1956, but mercury as the causative agent was identified only in 1959.

Locals in Minamata called it Cat Dancing Disease, because of abnormal uncontrolled body movement (=ataxia) seen in victims. The symptoms included numbness in limbs, muscle weakness, speach problem, etc at the onset of the disease followed soon by insanity, paralysis and death.