Decrease in the lethal effect of snake venom by serum of the opossum, Didelphis marsupialis.

Decrease in the lethal effect of several crotalid snake venoms were compared when diluted or mixed with opossum serum, normal horse serum, or normal dog serum and injected into mice. Normal dog and horse serum showed no protective qualities while opossum serum and diluted antivenin were approximately equivalent in their protective effect.