"Can Havana be purified? And if so, will such purification result in the eradication of yellow fever and malaria? Both questions can be answered affirmatively and positively. Havana is no dirtier than many another city has been. In England, in the olden time, the earthen floors were strewn with rushes. When these became sodden with filth beyond all endurance, fresh rushes were thrown over the old ones, and these in turn were buried, until the foul accumulation was several feet deep. Excrement was allowed to remain in and around the houses indefinitely, or was thrown into the streets regardless of consequences. In London, the frequent cry of, 'Ware below!' indicated that the household slops were about to be poured from an upper window. These conditions remained until repeated visits of the great sanitary teachers--the plague, the black death, the cholera, and other pestilences, which devastated cities and swept whole villages out of existence--had taught their hard lesson. On the continent the ignorance and neglect were, if possible, even greater. We have profited by the bitter experience of our ancestors; and no intelligent person questions the merit of sanitary works. But their true value is not yet fully appreciated, even by educated men whose interests are at stake. "The poison of yellow fever is ponderable. It clings to low levels and usually follows the lines of greatest humidity. Like malaria, it is more active--or at least more to be feared--by night than by day. The danger from it in any quarter of an infected locality depends upon the presence primarily of filth, secondarily of dampness; and it increases in direct proportion to the confinement and stagnation of the air. Infected cellars are more dangerous than infected rooms. The holds of ships are notorious hotbeds of the disease.