Suppose a house with a great central hall, into which a current of fresh, temperately warmed air is continually pouring. Each chamber opening upon this hall has a chimney up whose flue the rarefied air is constantly passing, drawing up with it all the foul and poisonous gases. That house is well ventilated, and in a way that need bring no dangerous draughts upon the most delicate invalid. For the better securing of privacy in sleeping-rooms, we have seen two doors employed, one of which is made with slats, like a window-blind, so that air is freely transmitted without exposing the interior. When we speak of fresh air, we insist on the full rigor of the term. It must not be the air of a cellar, heavily laden with the poisonous nitrogen of turnips and cabbages, but good, fresh, out-door air from a cold-air pipe so placed as not to get the lower stratum near the ground, where heavy damps and exhalations collect, but high up in just the clearest and most elastic region. The conclusion of the whole matter is, that, as all of man's and woman's peace and comfort, all their love, all their amiability, all their religion, have got to come to them, while they live in this world, through the medium of the brain,--and as black, uncleansed blood acts on the brain as a poison, and as no other than black, uncleansed blood can be got by the lungs out of impure air,--the first object of the man who builds a house is to secure a pure and healthy atmosphere therein. Therefore, in allotting expenses, set this down as a _must-be_: "Our house must have fresh air,--everywhere, at all times, winter and summer." Whether we have stone facings or no,--whether our parlor has cornices or marble mantels or no,--whether our doors are machine-made or hand-made. All our fixtures shall be of the plainest and simplest, but we will have fresh air. We will open our door with a latch and string, if we cannot afford lock and knob and fresh air too,--but in our house we will live cleanly and Christianly. We will no more breathe the foul air rejected from a neighbor's lungs than we will use a neighbor's tooth-brush and hair-brush. Such is the first essential of "our house,"--the first great element of human health and happiness,--AIR. "I say, Marianne," said Bob, "have we got fireplaces in our chambers?" "Mamma took care of that," said Marianne. "You may be quite sure," said I, "if your mother has had a hand in planning your house, that the ventilation is cared for." It must be confessed that Bob's principal idea in a house had been a Gothic library, and his mind had labored more on the possibility of adapting some favorite bits from the baronial antiquities to modern needs than on anything so terrestrial as air. Therefore he awoke as from a dream, and taking two or three monstrous inhalations, he seized the plans and began looking over them with new energy. Meanwhile I went on with my prelection. * * * * *