The next cheering find was that the worst enemies of the bacillus were our best friends. Sunlight will kill them just as certainly as it will give us new life. The germs of tuberculosis will live for weeks and even months in dark, damp, unventilated quarters, just precisely such surroundings as are provided for them in the inside bedrooms of our tenements, and the dark, cellar-like rooms of many a peasant's cottage or farmhouse. In bright sunlight they will perish in from three to six hours; in bright daylight in less than half a day. This is one of the factors that helps to explain the apparent paradox, that the dust collected from the floors and walls of tents and cottages in which consumptives were treated was almost entirely free from tuberculous bacilli, while dust taken from the walls of tenement houses, the floors of street-cars, the walls of churches and theatres in New York City, was found to be simply alive with them. One of the most important elements in the value of sunlight in the treatment of consumption is its powerful germicidal effect.
Closely allied to the discovery that sunlight and fresh air are fatal to the microörganisms of tuberculosis came the consoling fact that these bacilli, though most horribly ubiquitous and apparently infesting both the heavens above and the earth beneath, had neither wings nor legs, and were absolutely incapable of propelling themselves a fraction of an inch. They do not move--_they have to be carried_. More than this, like all other disease-germs, while incredibly tiny and infinitesimal, they have a definite weight of their own, and are subject to the law of gravity. They do not flit about hither and thither in the atmosphere, thistledown fashion, but rapidly fall to the floor of whatever room or receptacle they may be thrown in. And the problem of their transference is not that of direct carrying from one victim to the next, but the intermediate one of infected materials, such as are usually associated with visible dust or dirt. In short, keep dust or dirt from the floor, out of our food, away from our fingers or clothing or anything that can be brought to or near the mouth, and you will practically have abolished the possibility of the transference of tuberculosis. The consumptive himself is not a direct source of danger. It is only his filthy or unsanitary surroundings. Put a consumptive, who is careful of his sputum and cleanly in his habits, in a well-lighted, well-ventilated room, or, better still, out of doors, and there will be exceedingly little danger of any other member of his family or of those in the house with him contracting the disease. Wherever there is dirt or dust there is danger, and there almost only. Thorough and effective house-reform--not merely in tenements, alas! but in myriads of private houses as well--would abolish two-thirds of the spread of tuberculosis.