(1) From 1954 to 1956 the authors isolated 51 strains of cytopathogenic agents mostly from feces of patients with paralytic poliomyelitis using human embryonic skin-muscle tissue culture. As a result of typing we found 31 strains of type I (70%), 7 strains of type II (15%), 7 strains of type III (15%) and 6 untypable agents. 70 to 80 per cents of causative agents of paralytic poliomyelitis belonged to type I in Japan in the above period.
(2) Neutralization test using 100 TCD 50 of three types of poliovirus vs. undiluted and diluted (1:10) sera from healthy individuals was done on 209 specimens from Tokyo. The percentage positive was lowest at 6-11 months after birth, increasing rapidly, and the adult level (80-100%) was reached about 4 to 6 years of age. This pattern of the age distribution of antibody is almost equal to those obtained in Cairo, Egypt, and French Morocco. In the case of diluted sera the final level attained was 60-80 per cent, so that about 20 per cent of immune adults were considered having antibody titer less than 1:10.
(3) 46 per cent of paralytic polio occurred in the first year of life in Tokyo 1955, and steep increase of neutralizing antibody was seen among examinees belonging to the same age group. It means that paralytic sequelae are very likely to occur in the primary infection without protection of antibody.
(4) Analysis of antibody for one or more types of poliovirus in various age groups shows that infection by any one type interfere with heterotypic infections, in other words there exists some degree of cross immunity between heterotypes.
(5) Antibody titers of the pooled sera which were composed of an equal quantity of sera from individuals belonging to the same age group were minimum (antibody titer against type II and III were zero, but that of type I was 1:3 to 1:8) under one year of age, rose up to maximum (1:64 to 1:128) at 4 to 6 years of age, then declined a little and kept at a level (1:16 to 1:32) thereafter in Tokyo.
