The rebel commander called upon the brave old Governor to surrender, representing that he was entirely at his mercy, but this the Governor refused to do. The rebel ship then opened fire, and continued to fire without any possibility of injury to herself, until the Government vessel was sunk. The survivors reported that Governor Alban and most of his men were killed by the hostile fire before the ship went down. For many years the masts and upper works of this vessel could be seen at low tide projecting above the water. CHAPTER XX QUARANTINE SYSTEM Panama, from its situation and location, was peculiarly liable to infection from other places in both North and South America. It was the gateway through which a large traffic passed, and through which a continuous stream of travelers had been entering and departing for the previous four hundred years. After we had once freed it from yellow fever, it was very important that we should keep it free, and to do this we had to take such measures as would prevent a person in the early stages of yellow fever coming into Panama, and infecting the mosquitoes there, and thus starting an epidemic. It was possible, also, for a ship to come into a port with infected mosquitoes aboard. These infected mosquitoes might escape to the shore and in this way start the disease, or they might bite some non-immune visiting the ship, and cause this non-immune to develop yellow fever at his house in from three to six days after he had visited the ship. To protect ourselves against the introduction of yellow fever in the above ways, quarantine regulations were established. Any ship that had developed a case of yellow fever aboard was considered infected. We knew that if the case were developed aboard, she must have had infected mosquitoes there which had bitten the patient and caused the disease. The ship was, therefore, fumigated in such a way as to kill all mosquitoes. After she had been fumigated, we considered her safe. But though the ship could be rendered safe by the fumigation, some of the passengers or crew might have been bitten by the infected mosquitoes just before the fumigation of the ship, and such person might develop yellow fever during the succeeding six days. We therefore took all the non-immunes to our quarantine station, and kept them for six days. At the end of six days we allowed them to return to the ship. The vessel itself, with all the immunes aboard, was released from quarantine as soon as the fumigation had been completed. As I have said before, a person who has once had yellow fever is not liable to a second attack. Such person is known as an immune. To prove immunity, a passenger or member of the crew was required to present a written statement from some recognized authority stating that the writer knew that the person under consideration had suffered from an attack of yellow fever.