narrow slit, as in the case of the organ pipe.  If air from the lungs is sent through the narrow slit, the vocal cords or bands are thrown into rapid vibration and produce sound.  The pitch of the sound depends upon the tension of the stretched membranes, and since this can be altered by muscular action, the voice can be modulated at will.  In times of excitement, when the muscles of the body in general are in a state of great tension, the pitch is likely to be uncommonly high.

Women’s voices are higher than men’s because the vocal cords are shorter and finer; even though muscular tension is relaxed and the cords are made looser, the pitch of a woman’s voice does not fall so low as that of a man’s voice since his cords are naturally much longer and coarser.  The difference between a soprano and an alto voice is merely one of length and tension of the vocal cords.

Successful singing is possible only when the vocal cords are readily flexible and when the singer can supply a steady, continuous blast of air through the slit between the cords.  The hoarseness which frequently accompanies cold in the head is due to the thickening of the mucous membrane and to the filling up of the slit with mucus, because when this happens, the vocal cords cannot vibrate properly.

The sounds produced by the vocal cords are transformed into speech by the help of the tongue and lips, which modify the shape of the mouth cavity.  Some of the lower animals have a speaking apparatus similar to our own, but they cannot perfectly transform sound into speech.  The birds use their vocal cords to beautiful advantage in singing, far surpassing us in many ways, but the power of speech is lacking.

276.  The Ear.  The pulses created in the air by a sounding body are received by the ear and the impulses which they impart to the auditory nerve pass to the brain and we become conscious of a sound.  The ear is capable of marvelous discrimination and accuracy.  “In order to form an idea of the extent of this power imagine an auditor in a large music hall where a full band and chorus are performing.  Here, there are sounds mingled together of all varieties of pitch, loudness, and quality; stringed instruments, wood instruments, brass instruments, and voices, of many different kinds.  And in addition to these there may be all sorts of accidental and irregular sounds and noises, such as the trampling and shuffling of feet, the hum of voices, the rustle of dress, the creaking of doors, and many others.  Now it must be remembered that the only means the ear has of becoming aware of these simultaneous sounds is by the condensations and rarefactions which reach it; and yet when the sound wave meets the nerves, the nerves single out each individual element, and convey to the mind of the hearer, not only the tones and notes of every instrument in the orchestra, but the character of every accidental noise; and almost as distinctly as if each single tone or noise were heard alone.”—­POLE.