Want of cleanliness, then, in rooms _and_ wards, which you have to guard against, may arise in three ways. [Sidenote: Dirty air from without.] 1. Dirty air coming in from without, soiled by sewer emanations, the evaporation from dirty streets, smoke, bits of unburnt fuel, bits of straw, bits of horse dung. [Sidenote: Best kind of wall for a house.] If people would but cover the outside walls of their houses with plain or encaustic tiles, what an incalculable improvement would there be in light, cleanliness, dryness, warmth, and consequently economy. The play of a fire-engine would then effectually wash the outside of a house. This kind of _walling_ would stand next to paving in improving the health of towns. [Sidenote: Dirty air from within.] 2. Dirty air coming from within, from dust, which you often displace, but never remove. And this recalls what ought to be a _sine qua non_. Have as few ledges in your room or ward as possible. And under no pretence have any ledge whatever out-of sight. Dust accumulates there, and will never be wiped off. This is a certain way to soil the air. Besides this, the animal exhalations from your inmates saturate your furniture. And if you never clean your furniture properly, how can your rooms or wards be anything but musty? Ventilate as you please, the rooms will never be sweet. Besides this, there is a constant _degradation_, as it is called, taking place from everything except polished or glazed articles--_E.g._ in colouring certain green papers arsenic is used. Now in the very dust even, which is lying about in rooms hung with this kind of green paper, arsenic has been distinctly detected. You see your dust is anything but harmless; yet you will let such dust lie about your ledges for months, your rooms for ever. Again, the fire fills the room with coal-dust. [Sidenote: Dirty air from the carpet.] 3. Dirty air coming from the carpet. Above all, take care of the carpets, that the animal dirt left there by the feet of visitors does not stay there. Floors, unless the grain is filled up and polished, are just as bad. The smell from the floor of a school-room or ward, when any moisture brings out the organic matter by which it is saturated, might alone be enough to warn us of the mischief that is going on. [Sidenote: Remedies.] The outer air, then, can only be kept clean by sanitary improvements, and by consuming smoke. The expense in soap, which this single improvement would save, is quite incalculable. The inside air can only be kept clean by excessive care in the ways mentioned above--to rid the walls, carpets, furniture, ledges, &c., of the organic matter and dust--dust consisting greatly of this organic matter--with which they become saturated, and which is what really makes the room musty. Without cleanliness, you cannot have all the effect of ventilation; without ventilation, you can have no thorough cleanliness.