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 leads us to remove the barrier between the two kingdoms, and to consider minerals as endowed with a sort of rudimentary life, is the same as that which compels us to admit that there is no fundamental difference between natural phenomena. There are transitions between what lives and what does not, between the animate being and the brute body. And in the same way there are transitions between what thinks and what does not think, between what is thought and what is not thought, between the conscious and the unconscious. This idea of insensible transition, of a continuous path between apparent antitheses, at first arouses an insuperable opposition in minds not prepared for it by a long comparison of facts. It is slowly realized, and finally is accepted by those who, in the world of things, follow the infinity of gradations presented by natural phenomena. The principle of continuity comes at last to constitute, as one may say, a mental habit. Thus the man of science may be led, like the philosopher, to entertain the idea of a rudimentary form of life animating matter. He may, like the philosopher, be guided by this idea; he may attribute a priori to brute matter all the really essential qualities of living beings. But this must be on the condition that, assuming these properties to be common, he must afterwards demonstrate them by means of observation and experiment. He must show that molecules and atoms, far from being inert and dead masses, are in reality active elements, endowed with a kind of inferior life, which is manifested by all the transformations observed in brute matter, by attractions and repulsions, by movements in response to external stimuli, by variations of state and of equilibrium; and finally, by the systematic methods