508. _Railroad cars, cabins of steam and canal-boats, omnibuses, and stage-coaches, require ample ventilation._ In the construction of these public conveyances, too frequently, the only apparent design is, to seat the greatest number of persons, regardless of the quantity and character of the air to maintain health and even life. The character of the air is only realized when, from the fresh, pure air, we enter a crowded cabin of a boat or a closed coach; then the vitiated air from animal excretions and noxious gases is offensive, and frequently produces sickness. 509. The influence of habit is strikingly expressed by Birnan, in the "Art of Warming and Ventilating Rooms:" "Not the least remarkable example of the power of habit is its reconciling us to practices which, but for its influence, would be considered noxious and disgusting. We instinctively shun approach to the dirty, the squalid, and the diseased, and use no garment that may have been worn by another. We open sewers for matters that offend the sight or the smell, and contaminate the air. We carefully remove impurities from what we eat and drink, filter turbid water, and fastidiously avoid drinking from a cup that may have been pressed to the lips of a friend. On the other hand, we resort to places of assembly, and draw into our mouths air loaded with effluvia from the lungs, skin, and clothing of every individual in the promiscuous crowd--exhalations offensive, to a certain extent, from the most healthy individuals; but when arising from a living mass of skin and lungs, in all stages of evaporation, disease, and putridity,--prevented by the walls and ceiling from escaping--they are, when thus concentrated, in the highest degree deleterious and loathsome." -=-=-=-=-=-=-=-=-=-=-=-= What suggestion when a school-room is not ventilated? 507. What is said in regard to ventilating churches, concert halls, &c.? State the illustration. 508. What remarks relative to public conveyances? 509. State the influence of habit by Birnan. -=-=-=-=-=-=-=-=-=-=-=-= 510. _The sleeping-room should be so ventilated that the air in the morning will be as pure as when retiring to rest in the evening._ Ventilation of the room would prevent morning headaches, the want of appetite, and languor--so common among the feeble. The impure air of sleeping-rooms probably causes more deaths than intemperance. Look around the country, and those who are most exposed, who live in huts but little superior to the sheds that shelter the farmer's flocks, are found to be the most healthy and robust. Headaches, liver complaints, coughs, and a multitude of nervous affections, are almost unknown to them; not so with those who spend their days and nights in rooms in which the sashes of the windows are calked, or perchance doubled, to prevent the keen but healthy air of winter from entering their apartments. Disease and suffering are their constant companions. -=-=-=-=-=-=-=-=-=-=-=-=