In a previous communication (1921) experiments have been described showing the effect produced by continuously adding normal mice to a cage, the population of which is infected with bacilli of the group which includes B. gaertner and B. suipestifer. It was seen that under these circumstances the spread of infection progresses in a series of epidemic waves, and that the survival-time of any batch of mice varies according to the period at which they are introduced to the cage. It was further shown that, if such regular and continuous addition of susceptible animals be persisted in over long periods of time, all the micewill eventually succumb, while, if the addition of new individuals be discontinued, the epidemic will eventually subside, leaving a proportion of survivors who may remain in apparently good health over a considerable period.