But still the demonstration was not complete. It was necessary to prove by equally undeniable evidence that yellow fever is not conveyed by contagion with the clothes and persons of infected people. These experiments were even more trying and heroic than those which preceded. A small wooden hut, 14 by 20 feet, was prepared, and into this was stored a large amount of bedding and clothes which had been used and worn by persons suffering from the fever. The building was carefully guarded against the intrusion of mosquitoes, and a temperature of seventy-six degrees, with a sufficient moisture, maintained. For twenty consecutive days Dr. Clarke and his men went into this room, handled, wore, and slept in the contaminated clothing, although the stench was so offensive as to be almost appalling. They emerged from the ordeal in perfect health, proving beyond possibility of dispute that the disease was not contagious, and that the mosquito was the sole method of transmission. When distributing the credit for the new channel of world-traffic through the isthmus of Panama, let us not forget Dr. Lazear who sacrificed his life and the many others who cheerfully risked their lives to establish truths and facts without which the construction and continued operation of the canal would almost certainly have been impossible. One mosquito may look very much like another, but the _stegomyia_ and the _anopheles_ differ in many important respects. The latter finds its most favourable breeding-places in stagnant pools of fresh water, such as are left by the heavy rains of the isthmus. It is essentially a gnat of the country-side. The _stegomyia_, on the other hand, inclines to a more frivolous town life. Cisterns and tanks and other receptacles for storing water are his favourite haunts. In length of life and power of flight the species also differ, though these details are not yet fully ascertained. The _stegomyia_ is said to live three months. Dr. Cornish states that it becomes dangerous only by attacking man during the first three days of yellow fever, and that, even then, twelve days elapse before its bite is infectious. Six days after a man has been bitten by an infected _stegomyia_ he falls ill with yellow fever, and for the next three days he is capable of transmitting it to the healthy mosquito. Mr. Bishop informs us that if there is no fresh case of yellow fever within a period of sixty days after the latest one in an epidemic, it is a safe conclusion that the disease has been stamped out, because there is no mosquito alive to carry the parasite. After a period of ninety days all doubt on the subject is removed.[9] If a community, therefore, which has thus got rid of its last case of yellow fever could be completely isolated, yellow fever could never possibly return. It could only be reintroduced from outside. It should be possible, with a proper system of sanitation and quarantine, to free any district entirely from this awful scourge.