The view of the non-communication of leprosy by latent bacilli is further strengthened by the fact that there are places in Norway where many descendants of lepers live without one single one of them becoming leprous, as for example, in the town of Bergen where the descendants of lepers may certainly be numbered by thousands; and further, we have demonstrated by our investigations in North America, that of the numerous descendants of Norwegian lepers there, not one has developed the disease. But since about one hundred and seventy leprous Norwegians have emigrated to America, it may possibly be that the disease is spread by infection. There are indeed cases in America which have possibly arisen from infection, but they are not sufficiently definite to serve as arguments for its contagion. But even if leprosy be a contagious disease, one can easily understand how it should spread little, or not at all, in North America, when one compares the social condition and especially the cleanliness there with that in Norway, and probably especially with that of the districts in which leprosy is most prevalent. In North America the dwelling houses are roomy, so that the lepers whom we saw there had usually their own room, or at least their own bed; and everywhere, even among the Norwegians, great cleanliness is observed. And this is, according to our view, sufficient isolation in order, in most cases, to prevent the spread of the disease. That leprosy is really contagious is primarily evident from its nature as a bacillary disease. No one has been able to demonstrate the presence of the bacillus outside the human body, so that we may abandon the idea of a miasmatic origin.