One morning about daylight I got a message stating that her ladyship was in a most critical and desperate plight, as some time during the night she had gotten her wing caught in a mesh of the mosquito netting, and had struggled to free herself for so long a time that when she was discovered by the attendant in the morning, she was almost dead. I rapidly dressed and hurried to the hospital. Similar messages had been sent to Dr. Ross and Dr. Guiteras. We found her condition even worse than had been represented. Two or three of the doctors on the staff of the hospital had been promptly called in, and the services of several of our trained nurses had been likewise obtained. Her wing had been gently liberated from the mesh of the netting, and her ladyship laid upon a soft bed of cotton batting. The oil-stove was started up, and the room brought to a very hot summer temperature, but it was all of no avail. She finally ceased to kick about nine o’clock in the morning, and died with a larger attendance of doctors and nurses around her table than had ever been present around the deathbed of any mere human in the city of Havana. This account may sound somewhat exaggerated, but the scene still comes back to my mind’s eye very vividly, how earnest and serious we all were. A half-dozen of the leading practitioners of Havana were sitting around the deathbed of this mosquito, looking and feeling exceedingly mournful and depressed. And it was a very heavy blow to the Health Department of Havana. It was well on into the summer, the month of July, before we succeeded in getting another infected mosquito, and in proceeding with our vaccination work. Finally, we succeeded in infecting several mosquitoes, and bit with these mosquitoes sixteen persons, of whom eight developed the disease. Much to our alarm, several of these cases developed very violent symptoms, much more so than had occurred in any of the cases of the Army Board, with the exception of Lazear and Carroll. Three of these eight positive cases vaccinated by Dr. Guiteras died; one of those who died was a Miss Maas, a trained nurse from the United States, who requested to be allowed to get immunity in this way. Why our cases should have been so severe, and all of the cases of the Board so mild, no one has attempted to explain. It is a fact that during the hot summer weather the extrinsic period of incubation in the mosquito, that is, the time after which the mosquito bites the man sick with yellow fever until she herself is able to convey the disease, is considerably shorter than the same period during the cool winter months, this period in the summer months being from twelve to fourteen days, and in the winter months, from fifteen to twenty days. I am inclined to think that there is probably the same difference in the virulence of the infection developed by the mosquito in the hot summer months, and in the cool winter months.