412. The foregoing observations can be seen in a kind of reflected image and so confirmed because of the correspondence of the heart with love and of the lungs with the intellect, as discussed above. For since the heart corresponds to love, its offshoots-the arteries and veins-in that case correspond to affections, and in the lungs, affections for truth. And because the lungs have in them other vessels, called air passages, through which respiration takes place, therefore these vessels correspond to perceptions. [2] It should be rightly known that the arteries and veins in the lungs are not affections, and that the processes of respiration are not perceptions and thoughts, but that they are correspondent forms, for they function corresponsively or synchronously. It is the same as with the heart and lungs, which are not love and the intellect, but are correspondent forms. And since they are correspondent forms, one can be seen in the other. [3] One who from the study of anatomy is familiar with the whole structure of the lungs, if he compares it with the intellect, can clearly see that the intellect does not function on its own, does not perceive or think on its own, but does so wholly from affections belonging to love, which in the intellect are called an affection for knowing, for understanding, and for seeing a thing, as discussed above. For the states of the lungs all depend on blood from the heart, and from the vena cava and aorta; and the processes of respiration which take place in the bronchial ramifications occur in accordance with their state. For if the flow of blood ceases, respiration ceases. [4] Many more particulars could be disclosed from a comparison of the structure of the lungs with the intellect, to which they correspond. But because the science of anatomy is known to few, and to demonstrate or confirm something by means of things unknown puts the matter into a state of unintelligibility, therefore I am prevented from saying any more on this subject. From what I know of the structure of the lungs, I have been fully convinced that love through its affections joins itself to the intellect, and that the intellect does not join itself to any affection of love, but that it is joined to it in return by love, in order that the love may have a sensory life and an active life. [5] It must altogether be known, however, that a person possesses a double respiration, one of his spirit and the other of his body, and that the respiration of the spirit depends on fibers from the brain, and the respiration of the body on blood vessels from the heart, and on the vena cava and aorta. It is evident, furthermore, that thought produces respiration, and it is also evident that an affection belonging to love produces thought; for thought without an affection would be altogether like respiration without the heart, which is not possible. It is apparent therefore that an affection belonging to love joins itself to the thought belonging to the intellect, as we have said above. It is the same as with the heart in respect to the lungs.