The methyl mercury that enters the body mainly attacks the central nervous
system, including the brain., and causes various symptoms including numbness and
unsteadiness in the legs and hands, tiredness, ringing in the ears, narrowing of the
field of vision, loss of hearing, slurred speech, and awkward movements. Some early
severe victims of Minamata disease went insane, became unconscious, and died within
a month of the onset of the disease.