In Lessons X and XI, of the "Advanced Course" we called your attention to the Yogi teachings concerning _Akasa_ or Matter, and showed you that all forms of what we know as Matter are but different forms of manifestation of the principle called _Akasa_, or as the Western scientists call it, "Ether." This Ether or _Akasa_ is the finest, thinnest and most tenuous form of Matter, in fact it is Matter in its ultimate or fundamental form, the different forms of what we call Matter being but manifestations of this _Akasa_ or Ether, the apparent difference resulting from different rates of vibration, etc. We mention this fact here merely to bring clearly before your mind the fact of the Universality of Matter, to the end that you may realize that each and every particle of your physical body is but a portion of this great principle of the Universe, fresh from the great store-house, and just about returning to it again, for the atoms of the body are constantly changing. That which appears as your flesh to-day, may have been part of a plant a few days before, and may be part of some other living thing a few days hence. Constant change is going on, and what is yours to-day was someone's else yesterday, and still another's to-morrow. You do not own one atom of matter _personally_, it is all a part of the common supply, the stream flowing through you and through all Life, on and on forever. And so it is with the Vital Energy that you are using every moment of your life. You are constantly drawing upon the great Universal supply of _Prana_, then using what is given you, allowing the force to pass on to assume some other form. It is the property of all, and all you can do is to use what you need, and allow it to pass on. There is but one Force or Energy, and that is to be found everywhere at all times.