The resistance, which the womb offers to the fœtus that strikes against it, is wholly independent of density, and results only from the greater or less flexibility of its parietes. Cork is much less dense than mercury, and yet it offers to the finger, when pressed against it, a much greater resistance. [42] Of these four sources of sensation, the first, whatever Bichat may say, exists in the fœtus before birth, and the other three, do not exist some hours after; the eye is insensible to light, the ear to sound, and the taste is not really in exercise when the first food creates in the organ an unaccustomed sensation. [43] Philosophers and physiologists accord to the touch a great preeminence over the other senses. The senses of seeing, smelling and hearing are, say they, the sources of a thousand illusions. The touch alone is exempt from them, and even rectifies the errors which come from elsewhere; _the touch is the sense of reason_. It is undoubtedly a delightful prerogative; but let us see if it is incontestable. And first does the touch never deceive us? All children know an experiment which proves the contrary. If we cross two fingers of the same hand, and place in the angular space between their extremities a small body which touches both of them, the touch will give the sensation of two distinct bodies. It is then true that the touch may become a cause of errors; it no doubt serves to rectify those of the other senses, but do not these in their turn often defend us from the errors of the touch? If the sight were not almost constantly in exercise, the errors of touch would be much more numerous; we can judge of them by what we experience when we are in the dark. If we were to take from one man the use of his eyes, and from another that of his hands and the exercise of touch as much as possible, we should see which would be the most embarrassed, which would make the most false judgments. [44] This assertion is not correct, and the voice, at the earliest age, has consonances peculiar, not only to the species, but even to the individual. The man accustomed to the very striking differences of the articulate sounds of speech or the distinct sounds of music, distinguishes with difficulty the differences in cries; but the animals to whom the cry is the habitual medium of expression are not deceived in the same way; the ewe, in the midst of a whole flock, distinguishes the voice of her lamb, and this soon learns to recognize the voice of its mother. [45] The locomotive organs do not require a long education; as we see in animals whose organization, at the moment of birth, is no obstacle to motion. A young kid in an hour after, will stand on its legs, and before the end of the day we often see it skipping. The partridge runs as it comes out of the shell.