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Page:Popular Science Monthly Volume 24.djvu/511

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state of over-irritation, and return to their normal condition. We must, however, be careful not to fall into the common error of confounding stuttering with stammering. In stuttering the process of breathing is quite normal, and the defective speech arises only from inaptitude in the formation of sound; this defect of speech is, therefore, peculiar to children, idiots, and persons suffering from apoplexy.

Sighing, which is classed by Von Meyer as an unusual form of expiration, is better regarded as including the preceding inspiration also. A sigh is in fact a long breath, and, like a gape, is an involuntary spurt made to catch up with the demand for air. This is true even when it arises from depressing emotion. The expiration is often the more prominent part of the action, the rapidity with which the air flows out being due to a sudden cessation of the activity of the expiratory muscles, which commonly regulate, by retarding, the issuing stream of air. In sobbing, air is obtained by short, abrupt inspirations, and the tears which overflow into the nasal cavity assist in causing this air to produce sound.

Sneezing is the simplest of the purely expiratory noises. Just as the hiccough depends upon a single violent spasm during inspiration, so the sneeze is due to a single violent spasm during expiration, generally of the abdominal muscles, but, when very violent, of the other expiratory muscles also. It is a reflex action which occurs after an irritation of the mucous membrane lining the air-passages of the nose, and also after irritation of the optic nerve by a bright light. A few slight contractions of the abdominal muscles are at first suppressed by some short inspirations rapidly following each other without any intervening expiration; then follows a vigorous contraction of the abdominal muscles, by means of which the stream of air is violently driven out through the mouth and nose. In its passage through the nose, the air produces a well-known noise, which may, however, be connected with a sound produced in the vocal chords. We recognize the same peculiarity, though the action is voluntarily performed, in blowing the nose. Sneezing is not an observer of times and seasons, and often seems to choose the most inopportune moment for exhibiting its power. In such a case the impending catastrophe may be averted by pressing firmly upon some branch of the fifth nerve, say in the upper lip close under the nose.

Coughing and laughing are also due to a spasmodic contraction of the expiratory muscles. These acts differ from sneezing only in this respect, that, while in the latter expiration is accomplished by a single violent action, it is here characterized by a number of separate impulses of the expiratory muscles with small intervening pauses. In long-continued coughing or laughing, short inspirations, which, on account of their shortness and violence, often approach the verge of hiccoughing, are taken between the separate expirations, and, indeed, laughing after a full meal frequently leads to a fit of hiccoughs. Cough-