These problems belong on many sides to metaphysical speculation. They have been discussed by philosophers; they have been solved from time immemorial in different ways, for reasons and by arguments which it is not our purpose to examine here, and which, moreover, have not changed. But on some sides they belong to science, and must be tested in the light of its progress. Cuvier and Bichat, for example, considered that the forces in action in living beings were not only different from physico-mechanical forces, but were utterly opposed to them. We now know that this antagonism does not exist. The preceding doctrines, therefore, depend up to a certain point on experiment and observation. They are subject to the test of experiment and observation in proportion as the latter can give us information on the degree of difference or analogy presented by psychic, vital, and physico-chemical facts. Now, scientific investigations have thrown light on these points. There is no doubt that the analogies and the resemblances of these three orders of manifestations have appeared more and more numerous and striking as our knowledge has advanced. Hence it is that animism can count to-day but very few advocates in biological science. Vitalism in its different forms counts more supporters, but the great majority have adopted the physico-chemical theory. Both animism and vitalism separate from matter a directing principle which guides it. At bottom they are mythological theories somewhat similar to the paganism of old. The fable of Prometheus or the story of Pygmalion contains all that is essential. An immaterial principle, divine, stolen by the Titan from Jupiter, or obtained from Venus by the Cypriot sculptor, descends from Olympus and animates the form, till then inert, which has been carved in the marble or modelled in the clay. In a word, there is a human statue. It receives a breath of heavenly fire, a vital force, a divine spark, a soul, and behold! it is alive. But this breath can also leave it. An accident happens, a clot in a vein, a grain of lead in the brain—the life escapes, and all that is left is a corpse. A single instant has proved sufficient to destroy its fascination. This is how all men picture to their minds the scene of death. The breath escapes; something flies away, or flows away with the blood. The happy genius of the Greeks conceived a graceful image of this, for they represented the life or the soul in the form of a butterfly (Psyche) leaving the body, an ethereal butterfly, as it were, opening its sapphire wings. But what is this subtle and transient guest of the human statue, this passing stranger which makes of the living body an inhabited house? According to the animists it is the soul itself, in the sense in which the word is understood by philosophers; the immortal and reasoning soul. To the vitalists it is an inferior, subordinate soul; a soul, as it were, of secondary majesty, the vital force, or in a word, life.