The intracerebral mouse-protection test for pertussis vaccines

Abstract
Four series of tests, A, B, C and D, have been considered in detail. In the first two series, to obtain the values of the ImD 50, percentages of survivors were transformed into probits, and the best-fitting straight lines connecting the probits with the logarithms of the doses were obtained by the method of maximum likelihood. This is the most accurate method to use. These results showed that the error of the test was large, but there were no significant differences in the slope of the probitlog dose relation in the results of tests from any one laboratory. The slope (1·46 ± 0·09) obtained from series A was greater than that from series B (0·79 ± 0·06). with a consequent increase in accuracy.