1. The horse, apparently itself unsusceptible to poliomyelitis, can be stimulated in certain cases but not all to the production of virucidal antibodies.
2. The virucidal potency of such immune serum can be raised to a point comparable to that of human convalescent serum and when concentrated and refined exhibits a four-fold increase in potency.
3. Such concentrates have proved effective in the prevention of paralysis in inoculated monkeys when given intraspinously before the onset of paralysis.
4. Treatment has been found more effective when therapeutic serums are given through the spinal route.
5. Pooled serum from "normal" adult donors has proved effective in neutralizing virus but its potency is approximately one-half that of convalescent serum.