There are five bodies through which the soul experiences life, the physical body being the poorest of all, for it is born of matter, fed with matter, attracted to matter, finds its life in matter, and returns to matter. As it demands matter for its sustenance, so matter demands it in the end; this demand is called disease or death when this body loses its strength; and this is caused by the loss of energy of the nerves, which so to speak pull together and keep the flesh, bone, blood, and skin not only intact, but active and vigorous. It is the weakening of these nerves by exhaustion or by lack of sustenance, by lack of rest or by loss of energy in whatever manner, which is the cause of all disease.