567. There are two origins of heat, one the sun of heaven which is the Lord, and the other the sun of the world. The heat that is from the sun of heaven, that is, the Lord, is spiritual heat; and this in its essence is love (see above, n. 126-140); but the heat from the sun of the world is natural heat, and this in its essence is not love, but serves spiritual heat or love as a receptacle. Evidently love in its essence is heat, since it is love, in accord with its degree and quality, that gives heat to the mind, and thence to the body; and this man experiences as well in the winter as in the summer. The heating of the blood is from the same source. That the natural heat that springs from the sun of the world serves spiritual heat as a receptacle is evident from the heat of the body, which is excited by the heat of its spirit, and is a kind of substitute for that heat in the body. It is especially evident from the spring and summer heat in animals of every kind which then annually renew their loves.  It is not the natural heat that produces this effect, but it disposes their bodies to receive the heat that flows into them from the spiritual world; for the spiritual world flows into the natural as cause into effect. Whoever believes that natural heat produces these loves is much deceived, for influx is from the spiritual world into the natural world, and not from the natural world into the spiritual; and as all love belongs to the life itself it is spiritual.  Again, he who believes that any thing comes forth in the natural world without influx from the spiritual world is deceived, for what is natural comes forth and continues to exist only from what is spiritual. Furthermore, the subjects of the vegetable kingdom derive their germinations from influx out of the spiritual world. The natural heat of spring time and summer merely disposes the seeds into their natural forms by expanding and opening them so that influx from the spiritual world can there act as a cause. These things are mentioned to make clear that there are two kinds of heat, spiritual heat and natural heat; and that spiritual heat is from the sun of heaven and natural heat from the sun of the world, and that influx and consequent cooperation produce the effects that appear before the eyes in the world.#
# There is an influx from the spiritual world into the natural world (n. 6053-6058, 6189-6215, 6307-6327, 6466-6495, 6598-6626).
There is also an influx into the lives of animals (n. 5850).
And into the subjects of the vegetable kingdom (n. 3648).
This influx is a continual endeavor to act in accordance with the Divine order (n. 6211 at the end).