In a nursery there is the mother and child, and perhaps the nurse, to render the air impure by breathing, the fire and the lamp or candle to contribute to the same result, besides several other causes not yet mentioned. One of these is nearly related to the former. I allude to the fact that our skins, by perspiration and by other means, are a source of much impurity to the atmosphere; a fact which will be more fully explained and illustrated in the chapter on Bathing and Cleanliness. It is only necessary to say, in this place, that it is not the matter of perspiration alone which, issuing from the skin, renders the air impure; there are other exhalations more or less constantly going off from every living body, especially from the lungs; and carbonic acid gas is even formed all over the surface of the skin, as well as by means of the lungs. One needs no better proof that carbonic acid is formed on the surface of the body, than the fact that after the body has been closely covered all night, if you introduce a candle under the bed-clothes into this confined air, it will be quickly extinguished, because there is too much carbonic acid gas there, and too little oxygen. We may hence see at once the evil of covering the heads of infants when they lie down--a very common practice. The air, when pure, contains a little more than 20 parts of oxygen, and a little less than 80 of nitrogen. Breathing this air, as I have already shown, consumes the oxygen, which is so necessary to life and health, and leaves in its place an increase of nitrogen and carbonic acid gas, which are not necessary to health, and the latter of which is even positively injurious. But when the oxygen, instead of forming 20 or more parts in 100 of the atmosphere of the nursery, is reduced to 15 or 18 parts only, and the carbonic acid gas is increased from 1 or 2 parts in 100, to 5, 6, 8 or 10--when to this is added the other noxious exhalations from the body, and from the lamp or candle, fire-place, feather bed, stagnant fluids in the room, &c., &c.--is it any wonder that children, in the end, become sickly? What else could be expected but that the seeds of disease, thus early sown, should in due time spring up, and produce their appropriate fruits? It is sometimes said that fire in a room purifies it. It undoubtedly does so, to a certain extent, if fresh air be often admitted; but not otherwise. I have classed feather beds among the common causes of impurity. Dr. Dewees also condemns them, most decidedly; and gives substantial reasons for "driving them out of the nursery."