Of this eight hours is an outside limit, and from six to seven will generally be found sufficient, retiring to rest not later than 11 P. M., and rising from about 6 a. m. to 7.30. A. M., according to circumstances. The bedroom window should always be kept open at top and bottom, slightly in winter and wide in summer. Foul air generated by the human breath is never more hurtful than in a bedroom. Too much clothing should not be placed over the chest whilst sleeping, as by so doing respiration is more labored, and the legs and extremities, not the trunk, require extra covering for purposes of warmth. A mattress should be always used to sleep on, never a feather bed. High pillows and bolsters are very injurious. The natural height to which the head should be raised in sleep is about the thickness of the upper portion of the arm, which constitutes the pillow as designed by nature.