10. The bed of spiritual fluids which surrounds the Earth can be compared to the inferior beds of the atmosphere, heavier, more compact, less pure than the superior beds. These fluids are not homogeneous, they are a mixture of molecules of diverse qualities, amongst which are necessarily found the elementary molecules which form the base, but more or less changed in different states. The effect produced by these fluids will be according to the number of pure parts which they enclose. Such is, by comparison, rectified or mixed alcohol in different proportions of water or of other substances. Its specific weight is augmented by this mixture; while, at the same time, its force and inflammability are diminished, although there may be pure alcohol in all.
The spirits called to live in this midst draw from there their perispirit; but, according as the spirit becomes more or less purified, its perispirit is formed from the purest or grossest fluid of the world in which it is going to incarnate. The spirit produces there, always by comparison and not by assimilation, the effect of a chemical re-agent which attracts to it the molecules assimilable to its nature.
This capital fact results from it: that the inmost constitution of the perispirit is not identical with all incarnated or discarnated spirits which people the Earth or surrounding space. It is not the same with carnal bodies, which, as has been demonstrated, have been formed of the same elements whatever the superiority or inferiority of their spirits may have been. Also with us the effects produced by bodies are the same, they have the same necessities, while they differ by all that which is inherent in the perispirit.
Another result is, that the perispiritual envelope of the same spirit is modified with the moral progress of the latter at each incarnation, although incarnating himself in the same surroundings; that the superior spirits, incarnating themselves exceptionally by a mission into an inferior world, have a perispirit less gross than that of the natives of this world.