There is the same spontaneous training for the use of the voice as for movements. The vocal organ acquires dexterity just as the limbs do. The child learns how to produce such or such a sound just as it learns how to turn the head or the eyes, i. e., by constant efforts... By degrees consonants were added to the vowels, and the exclamations became more and more articulate. This process resulted in a sort of prattle of great diversity and completeness, which would be kept up for a quarter of an hour at a time, and repeated ten times a day. The sounds (vowel and consonant), which at first were vague and very hard to discriminate, became more and more like those uttered by adults, and the series of simple cries came to be, in some measure, like a foreign language which we do not understand...