494 MANUAL OF PHYSIOLOGY. 



ment, we set the expiratory, mouth, and general vocalizing mus- 

 cles in readiness for the proper application of the air blast by a 

 voluntary act ; but the exact tuning of the vocal cords is accom- 

 plished in some measure reflexly by impulses coming from the 

 ear to a special coordinating centre, the education of which is 

 commonly in advance of the volition centres,"and therefore can 

 only be controlled by the latter in persons specially educated to 

 music. Some persons who can sing a given note with promptness 

 and exactitude without any effort, would find much difficulty in 

 overcoming, by volition, the accuracy of this perfect reflex mech- 

 anism. In fact, a person with a good ear finds it difficult to sing 

 out of tune, even if he try. 



Though we feel that we have command over the pitch of our 

 sound-producing organ, we owe much to the aid of our sound- 

 appreciating organs and the nerve centres which they have in 

 connection with them. 



SPEECH. 



The variations in vocal sounds which give rise to speech are not 

 produced in the larynx, but in the throat, mouth, and nose. When 

 unaccompanied by any vocal sound, speech only gives rise to a 

 whisper; but when a vocal tone is at the same time produced, 

 we have the ordinary loud speaking. Since vocal tones can only 

 be produced by expiration, so we can only speak aloud by means 

 of an expiratory current of air ; but an inspiratory current may 

 be made to give rise to a kind of whisper. 



Speech is composed of two kinds of sounds, in one of which 

 the sounds must be accompanied by a vocal tone, and are 

 hence called " vowels ; " in the other no vocal tone is necessary, 

 but changes in shape take place in the resonating chambers, 

 so as to give rise to noises called consonants. As the pro- 

 nunciation of the consonants is usually accompanied by some 

 vowel sound, and, further, from the fact that the difference 

 between the vowels is brought about by changes in the shape 

 of the mouth, the distinction between the two sets of sound is 

 rather artificial than real. 



The production of the different vowel sounds depends upon 

 such a change being brought about in the shape of the mouth 



