492 MANUAL OF PHYSIOLOGY. 



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 pronunciation 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 

 cavity and aperture, that a resonator with a different individual 

 note is formed for each particular vowel. 



The sounds called consonants are caused by some check or im- 

 pediment being placed in the course of the blast of air issuing 

 from the air-passages. They may be classified, according to the 

 part at which the obstruction occurs, as follows: 



1. Labials, when the narrowing takes place at the lips, as in 

 pronouncing b, p,f, v. 



2. Dentals, when the tongue causes the obstruction by being 

 pushed against the hard palate or the teeth, as in t, d, s, I. 



3. Gutturals, when the posterior part of the tongue moves to- 

 wards the soft palate or pharynx, as in saying k, g, gh, ch, r. 



Consonants may also be divided into different groups, accord- 

 ing to the kind of movements which give rise to them. 



1. Explosives are produced by the sudden removal of the ob- 

 struction, as with p, d, k. 



2. Aspirates are continuous sounds caused by the passage of a 

 current of air through a narrow opening, which may be at the 

 lips, as in/, at the teeth as with s, or at the throat as in ch. 



