In the history of yellow fever, many curious cases of ship infection from this disease have occurred. During the fall of 1904, one of our warships, the _Boston_, spent several months in Panama Bay. While down the coast on gun practice, in January, 1905, she developed seven cases of yellow fever. She had been away from Panama such a length of time that the doctor knew that the cases must have received their infection aboard, and that therefore the ship was infected. The cases were well marked and most of them were severe, the doctor and one of the men dying of the disease. Nothing could be found in the sick records of the ship which would indicate that anyone belonging to the ship had contracted yellow fever ashore and developed a mild case, and thus infected the ship. All the cases were connected, directly or indirectly, with the wardroom, three of them being commissioned officers. As we were having at the time some yellow fever in Panama, the crew had not been allowed ashore. One or two of the officers, only, had been permitted to come into Panama for the transaction of necessary business. A short time before the ship had left the harbor, New Year’s Eve, 1904, they had given a ball aboard, which had been attended by a large number of the citizens of Panama. After a careful investigation of the matter, we concluded that some one of these persons was in the initial stages of a mild case of yellow fever. It is quite possible for such a person to be up and around without appreciating that he has the disease. This person, we concluded, was bitten by some of the stegomyia aboard. At the end of two weeks these stegomyia became infectious and gave the disease to the crew. Dr. G. A. Perry, of the Public Health Service, who had immediate charge of the work, found a small flat tub under the steps going down from the wardroom, in which stegomyia were breeding freely. This was the only place on the ship where larvæ were found, and this one piece of carelessness was responsible for the epidemic on the ship. All the mosquitoes aboard ship undoubtedly bred here. We could never find out why this tub was kept here, as the wardroom steward who was responsible, contracted the fever and died. The surgeon of the ship also died. The ship was carefully fumigated, under the supervision of Dr. Henry R. Carter, and no more cases occurred, though the ship immediately went to sea with all of her crew aboard, with the exception of the sick, who were brought to Ancon Hospital. As an instance of what a man sick with yellow fever may do in the way of going about, I will narrate here the case of one of our patients which will well illustrate this point.