discovering in the then habits of English living a _vera causa_ for the disease. Causes of Medieval Leprosy. What was there in the medieval manner of life to give rise to a certain number of cases of leprosy in all the countries of Europe? Granting that not all who were called _leprosi_ and _leprosae_, were actually the subjects of _lepra_ as correctly diagnosed, and that the misnomer was not unlikely to have been applied in the case of princes, nobles and great ecclesiastics, we have still to reckon with the apparition of leprosy among the people in medieval Europe and with its gradual extinction, an extinction that became absolute in most parts of Europe before the Modern period had begun. Of the “importation” of leprosy into Britain from some source outside there can be no serious thought; the words are a meaningless phrase, which no one with a real knowledge of the conditions, nature and affinities of leprosy would care to resort to. The varying types of diseases, or their existence at one time and absence at another, are a reflex of the variations in the life of the people--in food and drink, wages, domestic comfort, town life or country life, and the like. No one doubts that the birth-rate and the death-rate have had great variations from time to time, depending on the greater or less abundance of the means of subsistence, on overcrowding, or other things; and the variation in the birth-rate and death-rate is only the most obvious and numerically precise of a whole series of variations in vital phenomena, of which the successions, alternations, and novelties in the types of disease are the least simple, and least within the reach of mere notional apprehension or mere statistical management. The apparition and vanishing of leprosy in medieval Europe was one of those vital phenomena. It may be more easily apprehended by placing beside it a simple example from our own times.