Sleep with your windows open. Let the air circulate across your room
though not across your bed. Let the air be as pure as that out of doors.
Perform your exercises in bed with your windows open and with but little
covering. The vigorous exercises will bring greater warmth and you will
feel the desire to throw off the blanket. Some of the exercises, of
course, as lifting the legs, cannot be performed so well without
removing the covering.
The method of practicing the exercises as well as the amount, number and
character of them, depends greatly upon the health and the vitality of
the individual, but there must be a continual advance in the vigor and
the number of the exercises.