Abstract
When virulent Treponema pallidum are maintained in vitro for periods of days virulence may be lost earlier than motility. Motile treponemes, therefore, are not necessarily able to produce disease in the experimental animal. No clear correlation was found between either percentage motile nor duration of in vitro incubation and the infectivity of the suspension of treponemes. In determination of the in vitro effects of antitreponemai agents maintenance of virulence may be more useful criterion than maintenance of motility.