be ready for prolonged exertion, to open the mouth widely, so as to
draw a deep and rapid inspiration. When the next full expiration
follows, the mouth is slightly closed, and the lips, from causes
hereafter to be discussed, are somewhat protruded; and this form of the
mouth, if the voice be at all exerted, produces, according to
Helmholtz, the sound of the vowel _O_. Certainly a deep sound of a
prolonged _Oh!_ may be heard from a whole crowd of people immediately
after witnessing any astonishing spectacle. If, together with surprise,
pain be felt, there is a tendency to contract all the muscles of the
body, including those of the face, and the lips will then be drawn
back; and this will perhaps account for the sound becoming higher and
assuming the character of _Ah!_ or _Ach!_ As fear causes all the
muscles of the body to tremble, the voice naturally becomes tremulous,
and at the same time husky from the dryness of the mouth, owing to the
salivary glands failing to act. Why the laughter of man and the
tittering of monkeys should be a rapidly reiterated sound, cannot be
explained. During the utterance of these sounds, the mouth is
transversely elongated by the corners being drawn backwards and
upwards; and of this fact an explanation will be attempted in a future
chapter. But the whole subject of the differences of the sounds
produced under different states of the mind is so obscure, that I have
succeeded in throwing hardly any light on it; and the remarks which I
have made, have but little significance.
Sound Producing Quills from Tail of a Porcupine. Fig. 11
All the sounds hitherto noticed depend on the respiratory organs; but
sounds produced by wholly different means are likewise expressive.
Rabbits stamp loudly on the ground as a signal to their comrades; and
if a man knows how to do so properly, he may on a quiet evening hear
the rabbits answering him all around. These animals, as well as some
others, also stamp on the ground when made angry. Porcupines rattle
their quills and vibrate their tails when angered; and one behaved in
this manner when a live snake was placed in its compartment. The quills
on the tail are very different from those on the body: they are short,
hollow, thin like a goose-quill, with their ends transversely
truncated, so that they are open; they are supported on long, thin,
elastic foot-stalks. Now, when the tail is rapidly shaken, these hollow
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