If a child lie alone, place him fairly on his side in the middle of the bed; if it be winter time, see that his arms and hands be covered with the bedclothes; if it be summer, his hands might be allowed to be outside the clothes. In putting him down to sleep, you should ascertain that his face be not covered with the bedclothes; if it be, he will be poisoned with his own breath—the breath constantly giving off carbonic acid gas; which gas must, if his face be smothered in the clothes, be breathed—carbonic acid gas being highly poisonous. You can readily prove the existence of carbonic acid gas in the breathing, by simply breathing into a little lime-water; after breathing for a few seconds into it, a white film will form on the top; the carbonic acid gas from the breath unites with the lime of the lime-water, and the product of the white film is carbonate of lime. 187. _Do you advise a bed-room to be darkened at night?_ Certainly. A child sleeps sounder and sweeter in a dark than in a light room. There is nothing better, for the purpose of darkening a bed-room, than Venetian blinds. Remember, then, a well-ventilated, but a darkened chamber at night. The cot or the crib ought _not_ to face the window, “as the light is best behind.” [Sir Charles Locock in a _Letter_ to the Author.] 188. _Which is the best position for a child when sleeping—on his back, or on his side?_ His side. He ought to be accustomed to change about—on the right side one night, on the left another; and occasionally, for a change, he should lie on his back. By adopting this plan you will not only improve his figure, but likewise his health. Lying, night after night, in one position, would be likely to make him crooked. 189. _Do you advise, in the winter time, that there should be a fire in the night nursery?_ Certainly not, unless the weather be intensely cold. I dislike fires in bed-rooms, especially for children; they are very enervating, and make a child liable to catch cold. Cold weather is very bracing, particularly at night. “Generally speaking,” says the _Siecle_, “during winter, apartments are too much heated. The temperature in them ought not to exceed 16° Centigrade (59° Fahrenheit); and even in periods of great cold, scientific men declare that 12° or 14° had better not be exceeded. In the wards of hospitals, and in the chambers of the sick, care is taken not to have greater heat than 15°. Clerks in offices, and other persons of sedentary occupations, when the rooms in which they sit are too much heated, are liable to cerebral [brain] congestion and to pulmonary [lung] complaints. In bed-rooms, and particularly those of children, the temperature ought to be maintained rather low; it is even prudent only rarely to make fires in them, especially during the night.”