General Actions. - Lead and tin resemble one another to a considerable extent in their physiological action. After absorption into the circulation lead affects the muscles, involuntary and voluntary, and the central nervous system. Its action on muscle appears to be first irritant then paralysing. The irritant action on the muscle of the intestine leads to colic, and on the voluntary muscle to cramps in man. In animals, when the quantity administered in experiments at one time is much larger, paralysing action is more marked, and in frogs and rabbits, muscular weakness and rapid loss of irritability both in the voluntary muscles and heart are marked symptoms. In cats the paralysis of voluntary muscle is less marked, and in dogs it is absent.

The motor area of the central nervous system appears to be much more affected by lead than the sensory; and in dogs, cats, and pigeons choreic movements and even convulsions occur without impairment of sensation or consciousness. The irritation of the motor centres is succeeded by paralysis and death.

Tin has an action resembling lead in increasing the contractions of the intestinal canal and causing paralysis of the spinal cord. In rabbits it produces weakness and apparent recovery, and then paresis and death.1