This experience demonstrated to us most forcibly that vaccination could not take any prominent part in our preventive measures against yellow fever. While Dr. Guiteras was going on with his preparatory work at Las Animas and getting ready for his vaccinations, he invited to the hospital some fifteen or twenty members of the International Sanitary Congress who had expressed themselves as being particularly skeptical with regard to the mosquito theory of the transmission of yellow fever. This Congress assembled in Havana during the month of February, 1902. The laboratory at Las Animas was the room I have just described as being the home of the mosquito known as “Her Ladyship.” It was carefully screened with wire netting at all the windows, and the single door was protected by a vestibule which itself had double doors. This vestibule was built upon a platform some four feet above the ground and just outside the door of the laboratory. The visitors pretty well filled the small room. Dr. Guiteras started at one end of his laboratory, explaining that in this jar he had the eggs of the stegomyia mosquito, and invited his visitors to examine them; in the next jar, the larvæ; in the next, the pupæ; in the next, the young mosquito just born, and in the last jar, the mosquitoes which had passed their period of extrinsic incubation and were now ready to convey yellow fever. While handling this jar, the sleeve of mosquito-netting accidentally slipped off, and a dozen or more mosquitoes soared toward the ceiling of the room. Our visitors stood for a moment dumfounded, open-mouthed and wide-eyed. Then each one of the twenty, at the same moment, made a rush for the door. The vestibule was small and would hold only about four persons, so that the pressure from behind toppled it over onto the ground four feet below, and in a moment, there were some twenty gentlemen in a pile on the ground struggling to get as far as possible from these deadly lady mosquitoes. Dr. Guiteras afterwards assured us that his mosquitoes had never bitten a sick man and were not infected; that he was only demonstrating the processes of mosquito-breeding and infection that would have to be carried out in the vaccination process. Our visitors laughingly acknowledged that, at any rate, their subconscious selves had been convinced of the correctness of the theory of the mosquito transmission of yellow fever. CHAPTER V SANITARY WORK AT HAVANA The Army Board had demonstrated that the mosquito, to become infected, had always to bite some patient with yellow fever within the first three days of his disease. It was evident, therefore, that if we could prevent this being done in every case of yellow fever in Havana, the disease would disappear. This measure alone would be sufficient for eliminating yellow fever.