The experimental investigations of epidemic poliomyelitis, carried out during the past several months, have added a large number of important facts to the knowledge of this disease. These facts relate to the nature of the cause of the disease, the manner of its entrance into and exit from the body, the pathogenesis of the affection, and the existence of an enduring state of resistance to reinfection following an attack of the disease.1In the present communication we wish to present briefly certain further results which have been obtained in the course of experiments on active and passive immunization in respect to experimental poliomyelitis in monkeys. The virus which we are employing in our experiments was derived from Case K,2is in its twenty-fifth genaration in monkeys, and has attained a high degree of activity. Intracerebral inoculation of even minimal quantities of a filtrate3(0.02 to 0.01 c.c.) prepared from