444 VOICE. [CHAP. xxxi. 



voice-sounds, and as occurs in the case of other muscles, the 

 movements of those muscles whose office it is to regulate the 

 tension of the vocal chords, and govern the aperture of the glottis, 

 are much more rapid and perfect, much more under the control 

 of the will, and capable of executing more delicate movements in 

 some persons than in others ; and hence the wide difference between 

 individuals as to their capacity for singing and vocalization. Some- 

 thing in the difference of vocalizing power is due to minute and 

 inappreciable differences in the length of the vocal chords size 

 of glottis quantity of the elastic vocal chord tissue of the mucous 

 membrane (slight affections of which create hoarseness). 



The movements of the laryngeal muscles, as are the movements 

 of respiration, are much influenced by mental emotions. In 

 laughter, crying, sobbing, we have a combined excitement of re- 

 spiratory and vocal actions. 



In health, the emotions of grief, joy, and surprise, affect both 

 voice and speech -the latter more frequently and intensely than 

 the former. Diseases which involve more or less disturbance of 

 the centre of emotions, affect both voice and speech. Hysteria, 

 and chorea, may be referred to, the former generally affecting the 

 production of voice, the latter of speech. 



In certain affections of the brain, speech is impaired or alto- 

 gether destroyed, or at most limited to a monosyllable Yes or No. 

 This occurs under various conditions ; sometimes in consequence of 

 a chronic disease, sometimes of a shock : a diseased state of the 

 convolutions or hemispheres is the most frequent concomitant of 

 this symptom, but no precise part of the brain can be assigned as 

 a special organ of speech. 



In many diseases of a spasmodic or convulsive character, the 

 action of the muscles of the larynx is affected. In the spas- 

 modic croup or crowing inspiration of children, the chink of the 

 glottis is frequently so firmly closed, and for so long a time as to 

 endanger life. The peculiar "hoop" of hooping-cough, and the 

 curious voice-sounds so common and so varied in hysteria, show 

 that either these nerves themselves or the precise part of the 

 centre with which they are connected, are influenced by the mor- 

 bid action. In chorea the same want of power of co-ordinating 

 the movements is observed in the little muscles of the larynx as in 

 those which preside over the movements of the limbs and other 

 organs. 



In some of the conditions to which we have referred, it is diffi- 

 cult to say whether the motor nerve or its central origin is affected, 



