There were many reports on the neutralization test of poliomyelitis (polio) virus before 1939, as well as on the relationship between the neutralizing antibody and the illness. The animals available for the experiments of polio were only monkey before 1939, so that in any experiment animals were not used enough to estimate accurately the blood level of antibody because of their expense. However since Armstrong (1) was successful to transfer the “Lansing” strain of polio virus which had been isolated in monkey, first to the cotton rat and then to the swiss mouse, many mice were used for the neutralization test against the mouse-adapted strain, and the result would be more precise to discuss on the neutralizing antibody on the polio case.
It is well known that the higher positive rate of neutralization test of human sera against the “Lansing” strain of polio virus are found in the older age groups according to Turner (2) and Pait (3), the sera of 80% of children, less than 6 months old are capable of neutralizing the virus, while children from 6 months to 2 years of age have the positive rate in 20-30 per cent. With advances in ages an increasing percentages of individuals become positive in this test, and the sera of children between thee age of eight and twelve years have this property in 80%.
It was pointed out by Paul (4) that Japan was strongly contaminated by polio virus due to her poor sanitary condition. Well it is very important to determine how many Japanese in each age group has a neutralizing antibody against the mouse-adapted “Lansing” strain of polio virus following the subclinical infection.
The methods of neutralization test used by ntiany authors are not the same. They are summarized principally in the following :
1) by mixing the same quantities of undiluted serum and suspension of infects mouse brain and spinal cozd known to be active,
2) by mixing the same virus with sera 10, 3.2 or 2 fold diluted,
3) by mixing a series of 10 fold diluted virus with undiluted sera,
4) by mixing a series of 10 fold diluted virus with sera 10, 3.2 or 2 fold diluted.
Such mixtures are generally incubated for two hours and then injected intracerebrally into each group of mice.
Method 1) is the most simple and generally used. The point is that the virus employed in each experiment should be the same in an adequate virulence. For this purpose the virus emulsion should be kept in dry ice box in sealed ampules. If the virus is not of the same virulence it is impossible to compare the results obtained by many authors each other. For example Turner (5) used the virus suspension of 180 LD
50, Hammon (6) and Morgan (7) 10 LD
50 and Pait (3) 32 LD
50-. Method 2) is used to determine the titer of positive serum. Method 3) is for the determination of the negative serum. Method 4) isacombination of 2) and 3) . One example is shown in Table 1. Method 3) is generally used by us and sometimes combined with method 4) .
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