1968. It was said, moreover, that natural truths are vessels in which spiritual truths may be contained; for unless the objects or instrumental causes are adapted, the spiritual causes cannot be applied to them, as appears from many considerations, especially those drawn from the containing vessels of the whole body, as, for instance, that unless the blood-vessels with their membranes agree with the nature of the blood contained in them, they cannot hold the blood, much less can it act or be acted upon according to its nature and design. So likewise neither unless the blood-globules were such as they are, would the [animal] spirits and the life of the spirits be able to abide and live in them according to their nature and end; and thus also in all other things in the threefold kingdom and in the world. - 1748, May 16.