130 PHYSIOLOGY CHAP. 



animals, again, different organs or parts have the task of expression. 

 In the higher mammals it is the face which by the mobility of 

 its muscles betrays most expression, and in many mammals but 

 not in man the ears contribute greatly to expression by their 

 varied movements ; the nose, lips, and mouth play a considerable 

 part in physiognomy. In some animals, again, the movements of 

 the tail and feet are significant. Lastly, the different postures of 

 the body as a whole play a great part in expression. Painters, 

 sculptors, actors, alt-make special studies of the natural language, 

 both in animals and roan. They devote themselves to observing 

 and minutely analysing postures and deciphering their psycho- 

 logical significance, in order to reproduce them effectively in 

 works of art or dramatic representations. 



But the chief means by which the animal expresses its feelings, 

 wants, and passions is the voice, i.e. the inarticulate or scarcely 

 articulate sounds and noises which are characteristic of different 

 species. 



In deaf mutes the language of gesture attains a high develop- 

 ment, and is able to fulfil all the needs of social life. But under 

 normal conditions the mimetic language of man is almost always 

 accompanied by phonetic language, or speech, and merely serves 

 to reinforce and elucidate expression. 



Voice production is not the direct effect of muscular activity, 

 but is due to the vibrations produced in a particular apparatus, 

 the larynx, which is a true musical instrument. Nevertheless, as 

 it is muscular contraction which produces the degree of tension 

 in the vocal cords that is essential to the formation of the different 

 sounds, the study of phonation (speech) is closely connected with 

 the study of movements. 



The formation of words, i.e. articulate speech, is a more 

 complex process, which is not limited to the larynx, but also 

 depends on the production of non-musical noises by the current 

 of expired air as it passes through the pharynx, buccal cavity, 

 and nasal fossae. Consequently, laryngeal phonation is not in- 

 dispensable to conversation, any more than verbal articulation is 

 necessary to singing. It is possible to whisper without using 

 the vocal cords, and to sing vocally without words. 



I. Since the voice is an acoustic phenomenon with musical 

 characters, the organ which produces it may be considered as a 

 musical instrument. In order to understand its function in 

 speech, it is well to glance briefly at the fundamental principles 

 of the production and characteristics of tones in general. 



All elastic, solid, fluid, or gaseous bodies are capable of 

 vibrating so as to produce auditory sensations, that is, tones or 

 noises. A tone, according to Helmholtz, is any auditory sensation 

 produced by regular rhythmical vibrations ; a noise is a sensation 

 due to irregular and non-rhythmical vibrations. 



