As we explained in Chapter I., the development of all peoples has passed through a period during which medico-physical knowledge found expression exclusively in the teachings of religion. By theism we mean the system which endeavors to explain natural phenomena by supernatural causes. However, this view of nature, with its tinge of religion, did not as yet show any trace of superstition. It was rather the only justifiable conception of nature and thoroughly in keeping with the power of comprehension of man, until it began to dawn upon the mind that natural phenomena might be due to natural causes. This was the period of which we stated, in the beginning of this investigation, that faith became superstition and superstition became faith. It was during this time that the powers above were held accountable for all bodily ailments of mankind. It was their task most carefully to observe the functional processes of the human body in all its phases, and to protect their undisturbed continuance. But as the inhabitants of heaven, like the inhabitants of the earth, were subject to whims, it happened very often, unfortunately, that they attended to their task of protecting the undisturbed development of the vegetative as well as the animal functions of the body in a very unsatisfactory manner, sometimes, in fact, even purposely neglecting it. Thus disturbances occurred in the regular course of organic life, and this brought diseases into the world. If, therefore, the gods were directly responsible for the appearance of disease, it was palpably their duty to effect its elimination. Thus it came about that pathology and therapy were exclusively attended to by the gods. But in what light they regarded these medical duties of theirs, and how they performed them, were matters subject to very varying considerations, as expounded by the different religions of antiquity. The Babylonian considered the great god Marduk the expeller of all maladies, whereas Urugal, Namtor, and Nergal were recognized gods of pestilence. Similar ideas prevailed among the Egyptians. The cat-headed goddess Bubastis was believed to deal out to mothers the blessings of fertility. Ibis showed an especial interest in those human beings who were troubled with disturbances of digestion, and this interest found benevolent expression in the invention of the clyster.