This growth on the walls is a great hurt to the health of people living in the houses. It breeds disease, and keeps the moisture in the walls, so that the houses are damp and unwholesome. It is of no use to shut our windows at night, for the early morning chill that we hope thus to shut out is in the walls themselves. It is far better to leave the windows open, that fresh air may come in and drive out some of the poisonous vapors that rise from the walls and creep into the house. The walls of the house should be kept clean of mold. They should be scraped and whitewashed very often, and the green, unhealthy growth kept down. In the cities of Europe and America there are great sewer systems to take the waste and refuse from the houses and carry it far from the city. The sewers empty into the sea or into drainage canals, and thence to points where the sewage can be destroyed so that it will not endanger life. The city of Manila has some sewers. We can see the openings into them in the streets. They are small, square openings, covered with stone. But the sewers that run through the streets empty into the open moat that surrounds the walled city! It will become necessary, before many years, to fill this moat, to save the people of Manila from being killed by the gases that rise from it. Damp walls, damp floors, damp rooms close to the ground, make the very best sort of places for dirt to gather. It is not enough that walls should be scraped and floors cleaned once in a while; they must be kept clean all the time. This is why sanitary inspectors go about the city to examine houses and walls and report on their condition. We should be glad that they do this; for we know that if they are faithful about it, the city will be more healthful and many lives will be saved. The dirt that gathers in the streets is of many sorts. A great deal is made by the horses and carabaos, mules and oxen, that draw loads about the city. The wheels of the vehicles, too, grind the stone pavement to dust, and this is blown about by the wind. Dead leaves drop from the trees, choke up the gutters, and, left to themselves, will make sodden masses of decayed vegetation in corners. Waste paper blows about, and all sorts of unclean things are thrown into the streets by careless people. It takes a small army of laborers to keep the streets in order. They go over the city with brooms, shovels, and dust-boxes, and sweep and gather up refuse and dirt. They put it into carts and take it away to where it is loaded upon barges and sent out to sea, or used to fill in low places where it can do no harm. There is a great deal that each of us can do to help keep the streets clean. No one should ever do anything that is likely to leave any dirt about them. Banana and orange peel should never be thrown on the sidewalk. This is not only a dirty and untidy trick, but often a bit of peel does serious mischief; a person may step upon one, slip, and get a very dangerous fall.