Statistical aspects of the treponemal counts in the TPI test.

A method of counting treponemes in randomly selected visual fields is described. It was found that Treponema pallidum is distributed as a Poisson distribution among the visual fields and also among samples drawn from the same suspension. Immobilized treponemes are binomally distributed among the total number of treponemes. Application of the parameters of the Poisson and the binomial distributions should be made in order to determine the dosage of T. pallidum in animal experimentation and to evaluate the outcome of the TPI test. Some statistical aspects of the investigation of treponemal survival are presented.