e significance both are by all means
indispensable. For, the person born blind does not get the significance
of words pertaining to light and color. For him, therefore, a large
class of conceptions, an extensive portion of the vocabulary of his
language, remains empty sound. To the one born deaf there is likewise an
extensive district of conceptions closed, inasmuch as all words
pertaining to tone and noise remain unintelligible to him.

Moreover, those born blind and deaf, or those born blind and becoming
deaf very early, or those born deaf and becoming blind very early,
though they may possess ever so good intelligence, and perhaps even
learn to write letters, as did the famous Laura Bridgman, will
invariably understand only a small part of the vocabulary of their
language, and will not articulate correctly.

Those born deaf are precisely the ones that show plainly how necessary
hearing is for the acquirement of perfectly articulate speech. One who
is deaf from birth does not even learn to speak half a dozen sounds
correctly without assistance, and the loss of speech that regularly
follows deafness coming on in children who have already learned to
speak, shows how inseparably the learning and the development of perfect
articulation are bound up with the hearing. Even the deafness that comes
on in maturer years injures essentially the agreeable tone, often also
the intelligibility, of the utterance.

2. The Organic Conditions of Learning to Speak.

How is it, now, with the normal child, who is learning to speak? How is
it as to the existence and practicability of the nervous conduction, and
the genesis of the centers?

In order to decide these questions, a further extension of the diagram
is necessary (Fig. 3).

[Illustration: FIG. 3.]

For the last diagram deals only with the hearing and pronouncing of
sounds, syllables, and single words, not with the grammatical formation
and syntactical grouping of these; there must further be a center of
higher rank, the _dictorium_, or center of diction (Kussmaul), brought
into connection with the centers L S and W. And, on the one hand, the
word-image acquired (by hearing) must be at the disposition of the
diction-center, an excitation, therefore, passing from W to D (through
_m_); on the other hand, an impulse must go out from the diction-center
to pronounce the word that is formed and placed so as to correspond to
the sense (through _n_). The same is true for syllables