420. The like is imaged in the lungs, whose arteries and veins correspond to the affections belonging to love, and whose respiratory processes correspond to the perceptions and thoughts belonging to the intellect, as we said above. It is clear from a good deal of empirical observation that the heart's blood purifies itself of unassimilated elements in the lungs, and that it also nourishes itself with beneficial elements from the air inhaled. That the blood purifies itself of unassimilated elements in the lungs is clear not only from the nature of the blood flowing in, which is venous and therefore filled with chyle extracted from ingested foodstuffs and alcoholic spirits, but also from the moisture of their exhalations and the perceptible odor of those foodstuffs and spirits to the nostrils of others, and likewise from the diminished amount of blood flowing back [through the left atrium] into the left ventricle of the heart. [2] That the blood nourishes itself with beneficial elements from the air inhaled is clear from the immense amount of odors and exhalations continually emanating from fields, gardens and woodlands; from the immense amount of various kinds of salts contained in the moisture evaporating from the ground, streams and ponds; and from the immense amount of exhalations and effluvia arising from people and animals, with which the air is permeated. It cannot be denied that these elements flow into the lungs with the inhaled air, and because this cannot be denied, neither can it be denied that the blood draws from them such elements as are beneficial to it; and those elements are beneficial to it which correspond to the affections of its love. We accordingly find in the tiny sacs or inmost constituents of the lungs an abundance of capillaries with orifices that absorb such elements. We find, too, that the blood flowing back [through the left atrium] into the left ventricle of the heart has been transformed into arterial blood and become brighter. These observations confirm that the blood purifies itself of heterogeneous elements in the lungs, and that it nourishes itself with homogeneous ones. [3] The fact that the blood purifies and nourishes itself in the lungs in a manner corresponding to that of the affections of the mind is as yet unknown, but it is well known in the spiritual world. For the angels who dwell in the heavens take delight only in odors that correspond to their love of wisdom, whereas spirits in hell take delight only in odors that correspond to love opposed to wisdom. The latter odors are stenches, while the former are fragrances. It follows therefore that people in the world permeate their blood with similar elements according to the correspondence of these with the affections of their love. For what a person's spirit loves, the blood correspondingly hungers for and by the process of respiration takes in. It flows from this correspondence that a person is purified in respect to his love if he loves wisdom, and that he becomes polluted if he does not love it. A person's purification is accomplished, moreover, wholly through truths that are matters of wisdom. And a person's pollution is brought about wholly through falsities that are opposed to truths of wisdom.