2153. The writings of Liebig having proved the important fact that plants derive a considerable portion of their food from the air, and that consequently a regular supply of fresh air is as necessary to the health of plants as a regular supply of fresh water, threw quite a new light on the subject of ventilation; and it was now understood why plants deprived of fresh air became debilitated, lost their leaves, and finally died; and, in short, a distinction was made between mere ventilation, or the letting out of impure vapours, and what Dr. Lindley very properly calls aeration, or the admission of currents of fresh air at a temperature suitable to that already existing in the house.
