* The universal cosmic fluid is the fundamental constituent of all matter. 

* It assumes two extreme states, with a gradient of variations within each state and between the two. One state is that of materialization, which gives rise to phenomena of the visible (material) world. The second state is that of etherealization and gives rise to the phenomena of the invisible world. 

* All the varieties and modifications found along the above mentioned gradient constitute derivatives of the initial, basic element.  These derivatives are known as fluids.  These fluids, whether tangible/perceptible to us or not, are all considered to be matter.  They can be found in an infinite range of degrees of purity, from a starting point of absolute purity, all the way to that of transformation, in a way, a "condensation", into that which is tangible to us.  

* Modifications of the cosmic fluid, while still in the state of etherealization, form an infinite variety of distinct fluids with varying levels of purity.  These are referred to as spiritual fluids and form the material of the spiritual world. 

* Many of these spiritual fluids escape the perception of our human senses and instruments. Others are intimately tied to the corporeal life. The latter are the fluids that are closest to the point of materialization and the least pure.  They make up what is referred to as the spiritual atmosphere of the Earth, and they are in constant interaction with the material realm, whereby they affect, and are affected by, the beings that inhabit it.

 Click HERE to read in more detail  about The Universal Cosmic Fluid in an another excerpt from Allan Kardec's "Genesis".