sally acknowledged.

Further, it results from the abundance of clinical material, that the
acoustic-center K must be divided into a sound-center L, a
syllable-center S, a word-center W, each of which may be in itself
defective, for cases have been observed in which sounds were still
recognized and reproduced, but not syllables and words, also cases in
which sounds and syllables could be dealt with but no words; and,
finally, cases in which all these were wanting. The original diagram
is thereby considerably complicated, as the simple path of connection
between K and M has added to it the arcs L S M and L S W M (Fig. 2).

[Illustration: FIG. 2.]

The surest test of the perfect condition of all the segments is afforded
by the repetition of sounds, syllables, and words pronounced by others.

Syllables and sounds, but no words, can be pronounced if W is missing
or the path S W or W M is interrupted; no syllables if S is missing or
L S or S M is interrupted. If L is missing, then nothing can be
repeated from hearing. If L M is interrupted, then syllables and words
are more easily repeated than simple sounds, so far as the latter are
not syllables. If L S is interrupted, then simple sounds only can be
repeated. All these abnormal states have been actually observed. The
proofs are to be found in Kussmaul's classic work on the disturbances
of speech (1877). Even the strange case appears in which, L M being
impracticable, syllables are more easily repeated than simple sounds.

If _a_ is interrupted before the acquirement of speech, and thus chronic
deafness is present in very early childhood, articulation may still be
learned through visual and tactile impressions; but in this case the
sound-center L is not developed. Another, a sound-touch-center, comes in
its place in deaf-mutes when they are instructed, chiefly through the
tactile sensations of the tongue; and, when they are instructed in
reading (and writing), a sound-sight-(or letter) center. This last is,
on the contrary, wanting to those born blind; and both are wanting to
those born blind and deaf. Instead is formed in them through careful
instruction, by means of the tactile sensations of the finger-tips, a
center for signs of sound that are known by touch (as with the printed
text for the blind).

Accordingly, the eye and ear are not absolutely indispensable to the
acquirement of a verbal language; but for the thorough learning of the
verbal language in its entir