Like malaria, the disease is one requiring a hot climate, generally because it is favorable to mosquito growth. It is most common in the seacoast cities of the South, and is probably transmitted often by mosquitoes brought on board ship. Since Havana has been cleaned up by Americans, the danger formerly existing from intercourse with that city has ceased, although only three years ago the writer stopped in a hotel at Havana, where two persons had died of yellow fever a week before. The smell of disinfectants in the hotel was so great that not a fly or insect of any sort was visible, and no other hotel in the city could have been safer or more comfortable. It has been proved positively that yellow fever cannot be transmitted by direct contact, since, in the interests of science, volunteers have slept in beds from which the dead from yellow fever had just been removed without contracting the disease. That the infection is due only to mosquitoes is proved by the fact that later, when bitten by mosquitoes, they succumbed to the disease. It requires about two weeks for the disease to pass through its regular stages in the body of the mosquito, so that there is no possibility of its transmission for that time after the mosquito has come in contact with a yellow fever patient. The symptoms of yellow fever are characteristic and very severe. The eyes first become bloodshot and, in the course of two days, yellow, whence the name of the disease. Severe vomiting is also characteristic, the discharge being sometimes discolored like coffee or even tar and known as black vomit. The skin appears yellow, a condition which lasts for some time and is particularly noticeable if by the pressure of the finger on the skin the blood is made to recede. Among persons previously in good health, the death-rate is about that of typhoid fever, but among those in unfavorable surroundings and among those given to the use of alcohol, the rate will be much higher. Practically, it may be expected that this disease, like malaria, will disappear from the face of the earth. When the only requirement is the destruction of the mosquitoes and when mosquitoes can be so easily killed as already explained, it is only a question of time before mosquitoes and the diseases they cause will be stamped out. In Havana, before 1901, the number of the deaths yearly was about 750. In the year after the American intervention, when Colonel Gorgas, by military command, insisted on the thorough cleaning of the houses and the general use of kerosene in all drains and cesspools, there was not one single death. _Hookworm disease._