Cadmium is taken up by terrestrial snails living in an environment with a relatively high cadmium concentration. The metal becomes bound to protein with a molecular weight of approximately 22,000 daltons. This cadmium-protein complex concentrates in the digestive gland and is present in a form which is soluble in water, (though difficult to extract efficiently). That no efficient excretion mechanism exists for this soluble complex implies that it cannot traverse the cell wall. The failure to 450