But this adaptation of the pains of Tartarus to contemporary physics could not save them from philosophical criticism. While the pagan priests, to the terror of credulous minds, imagined more and more inhuman punishments for the guilty souls, the reaction of reason against these cruel inventions necessarily gathered strength. We have seen elsewhere how the polemics of philosophers forcibly attacked these life-poisoning beliefs and succeeded in a great measure in destroying them.[438] Even those who did not deny the future life rejected these fables of hell. There was an attempt to save the principle of posthumous retribution by replacing the doctrine of chastisement in Hades by that of the metempsychosis. We now will try, while considering this theory of transmigration in its various aspects, to show how such substitution was effected. * * * * * The mind of savages does not, like our science, distinguish between three kingdoms of nature. It supposes the same energy to animate all the beings who surround us, all of whom are taken to be like ourselves. The primitives often attribute human or even divine intelligence to beasts; and the belief is found throughout the two hemispheres that the spirits of the dead can incarnate themselves in animals and even lodge in plants. Men refrain from the slaughter or gathering of certain species, from eating their flesh or fruit, for fear of hurting a chief or relative who has gone to inhabit them. This animistic basis is common to a number of different peoples and is at the foundation of the system of metempsychosis. But that which makes the grandeur of this theory, which won countless adepts throughout the centuries and the world, is that it transformed this naïve idea, which had no moral bearing, into a doctrine of retribution and liberation. To come back to the earth, to imprison itself in a body which soiled and tortured it, became a punishment inflicted on the guilty soul. The soul could not attain to supreme felicity until it had purified itself by long suffering and had gradually, through a cycle of rebirths, freed itself from carnal passions.