496. That which a man receives with freedom remains, because his will accepts it and appropriates it, and because it enters his love, and the love acknowledges it as its own, and by means of it is formed. This shall be illustrated by comparisons, in which, because they are taken from natural things, heat will be substituted for love. It is well known that by means of heat, and according to the amount of it, the doors are opened in every plant, and as these are opened the plant inwardly returns into the form of its nature, spontaneously partakes of its proper nutriment, retains what is suitable, and grows. It is the same with a beast; all that it selects and eats from the love of nutrition which is called appetite, is added to its body, and thus remains. That which is suitable is continually added to the body, because all its components are perpetually renewed. This is known to be so, although by few.
 Also with beasts heat opens all parts of the body, and causes their natural love to act freely. This is why in spring and summer they enter and return into the instinct of propagating and rearing their young, which they do from the utmost freedom, because to do so belongs to the ruling love implanted in them by creation for the sake of preserving the universe in the state in which it was created.
 The freedom of love may be illustrated by this freedom induced by heat, because love produces heat, as is evident from its effects, for man is enkindled, heated, and inflamed as love is exalted to zeal, or to a blaze of anger. The heat of the blood or the vital heat of men, and of animals in general, is from no other source. It is because of this correspondence that it is by heat that the bodily parts are adapted to receive freely those things to which the love aspires.
 In such equilibrium and consequent freedom are all things that are within man. In such freedom the heart propels its blood upward and downward alike, the mesentery distributes its chyle, the liver does its work for the blood, the kidneys secrete, the glands filter and so on. If this equilibrium were to suffer the member would sicken, and would labor under a paralysis or loss of strength; and herein equilibrium and freedom are one. There is not a substance in the created universe that does not tend to equilibrium, in order that it may be in freedom.