This successful sanitary and hygienic work, which brought about practically the complete obliteration of leprosy in the Middle Ages, furnished the first example of the possibility of eradicating a disease that has once become a serious scourge to mankind. That this should have been accomplished by a movement that had its greatest source in the thirteenth century is all the more surprising, since we are usually accustomed to think of the people of the times as sadly lacking in any interest in sanitary matters. The role of the Popes in the matter is another striking feature well worthy of note. The significance of the success of this segregation method was lost upon men down almost to our own time. This was unfortunately because it was considered that most of the epidemic diseases were conveyed by the air. They were thought infectious and due to a climatic condition rather than contagious, that is, conveyed by actual {276} contact with the person having the disease or something that had touched him, which is the view now held. With the beginning of the crusade against tuberculosis in the later nineteenth century, however, the most encouraging factor for those engaged in it was the history of the success of segregation methods and careful prevention of the spread of the disease, which had been pursued against leprosy. In a word, the lessons in sanitation and prophylaxis of the thirteenth century are only now bearing fruit because the intervening centuries did not have sufficient knowledge to realize their import and take advantage of them.