The evidence on behalf of a naturalistic explanation of religious phenomena has been purposely stated in a suggestive rather than in an exhaustive manner. The main lines of evidence are threefold. First, there is the indisputable fact that in the lower stages of culture all mental and bodily diseases are universally attributed to spiritual agency. This explanation holds the field; it is the only one possible at the time, and it is not replaced until a comparatively late stage of human history. But of special importance is the fact that a belief does not die out suddenly. It is only destroyed very slowly, and even after the facts upon which the belief was originally based have been otherwise interpreted, the attitude of mind engendered by the long reign of a belief remains. It has by that time become part of the intellectual environment. Theories of a quasi-philosophic or quasi-scientific character are elaborated, and give to the original belief something of a rational air. Even to-day the extent to which superstitious practices still gather round the subject of disease is known only to the curious in such matters. Not that the original reason is given for the practice. In nearly every case a different one is invented. To take only a single example. We still find saffron tea largely used in cases of measles. All medical men are aware that it possesses not the slightest curative value. Students of folklore are aware that it has its origin in the theory of sympathetic cures. Its redeeming feature is that it is harmless; so we find it still in common use, and the recovery of a child from measles is often enough attributed to the potency of the concoction. So with the relation of disease to the persistence of the belief in the supernatural. The conclusion that disease--whether bodily or mental--is due to the agency of spirits is one that follows from the existence of the religious idea; but in turn the observed facts react and strengthen the religious belief. Every case of disease becomes to the primitive mind an unanswerable proof in favour of the original hypothesis. The disease is there, and the only explanation possible is in terms of the animistic idea. And all the time the religious idea is becoming more deeply embedded in the social consciousness, more firmly established as a social fact.