not be solved by the most important means possessed by physiology,
vivisection. And the speechless condition in which every human being is
born can not be regarded as a disease that may be healed by instruction,
as is the case with certain forms of acquired aphasia. A set of other
accomplishments, such as swimming, riding, fencing, piano-playing, the
acquirement of which is physiological, are learned like articulate
speech, and nobody calls the person that can not swim an anomaly on that
account. The _inability to appropriate_ to one's self these and other
co-ordinated muscular movements, this alone is abnormal. But we can not
tell in advance in the case of any new-born child whether he will learn
to speak or not, just as in the case of one who has suffered an
obstruction of speech or has entirely lost speech, it is not certain
whether he will ever recover it.

In this the normal child that does _not yet_ speak perfectly,
resembles the diseased adult who, for any cause, _no longer_ has
command of language. And to compare these two with each other is the
more important, as at present no other empirical way is open to us for
investigating the nature of the process of learning to speak; but this
way conducts us, fortunately, through pathology, to solid, important
physiological conclusions.

1. Disturbances of Speech in Adults.

The command of language comprises, on the one hand, the understanding of
what is spoken; on the other hand, the utterance of what is thought. It
is at the height of its performance in free, intelligible, connected
speech. Everything that disturbs the _understanding of words heard_ must
be designated disturbance of speech equally with everything that
disturbs _the production of words_ and sentences.

By means of excellent investigations made by many persons, especially by
Broca, Wernicke, Kussmaul, it has become possible to make a topical
division of most of the observed disturbances of speech of both kinds.
In the first class, which comprises the _impressive_ processes, we have
to consider every functional disturbance of the peripheral ear, of the
auditory nerve and of the central ends of the auditory nerve; in the
second class, viz., the _expressive_ processes, we consider every
functional disturbance of the apparatus required for articulation,
including the nerves belonging to this in their whole extent, in
particular the hypoglossus, as motor nerve of the tongue, and certain
parts of the cere