423. That love purified by the wisdom in the understanding becomes spiritual and celestial cannot be seen so clearly by their correspondence with the heart and lungs, because no one can see the quality of the blood by which the lungs are kept in their state of respiration. The blood may abound in impurities, and yet not be distinguishable from pure blood. Moreover, the respiration of a merely natural man appears the same as the respiration of a spiritual man. But the difference is clearly discerned in heaven, for there every one respires according to the marriage of love and wisdom; therefore as angels are recognized according to that marriage, so are they recognized according to their respiration. For this reason it is that when one who is not in that marriage enters heaven, he is seized with anguish in the breast, and struggles for breath like a man in the agonies of death; such persons, therefore throw themselves headlong from the place, nor do they find rest until they are among those who are in a respiration similar to their own; for then by correspondence they are in similar affection, and therefore in similar thought. From all this it can be seen that with the spiritual man it is the purer blood, called by some the animal spirit, which is purified; and that it is purified so far as the man is in the marriage of love and wisdom. It is this purer blood which corresponds most nearly to that marriage; and because this blood inflows into the blood of the body, it follows that the latter blood is also purified by means of 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.