423. That love purified by wisdom in the understanding becomes spiritual and celestial cannot be seen through its correspondence with the heart and lungs, because no one can see the quality of the blood by which the lungs are maintained in a state of respiration. The blood may abound in impurities, and yet be indistinguishable from pure blood. Moreover the respiration of a merely natural man appears the same as that of a spiritual man, but yet the difference is clearly discerned in heaven, for there everyone breathes in accordance with the marriage of love and wisdom; on this account, as angels are recognized by that marriage, they are recognized also by the breathing. This is why, when anyone enters heaven who is not in that marriage, he is seized with anguish in the breast, and struggles for breath like those in the agony of death; for which reason also he throws himself headlong from the place and does not rest until he finds himself among those with respiration similar to his own; for then by correspondence they are in similar affection and therefore in similar thought. From these things it can be established that with the spiritual man, it is his purer blood, called by some the animal spirit, which is purified; and that it is purified to the degree the man is in the marriage of love and wisdom. It is this purer blood which corresponds most nearly to this marriage, and since it flows into the blood of the body, it follows that the latter blood also is purified by it. The reverse is true of those in whom love is defiled in the understanding, but, as was said, no one can test this by any experiment on the blood, but he can by observing the affections of love, since these correspond to the blood.