Chap. IV. IN ANIMALS. 91 



trate to a distance. For Helmholtz lias shown 7 that, 

 owing to the shape of the internal cavity of the human 

 ear and its consequent power of resonance, high notes 

 produce a particularly strong impression. When male 

 animals utter sounds in order to please the females, they 

 would naturally employ those which are sweet to the 

 ears of the species; and it appears that the same sounds 

 are often pleasing to widely different animals, owing to 

 the similarity of their nervous systems, as we ourselves 

 perceive in the singing of birds and even in the chirping 

 of certain tree-frogs giving us pleasure. On the other 

 hand, sounds produced in order to strike terror into an 

 enemy, would naturally be harsh or displeasing. 



"Whether the principle of antithesis has come into 

 play with sounds, as might perhaps have been expected, 

 is doubtful. The interrupted, laughing or tittering 

 sounds made by man and by various kinds of monkeys 

 when pleased, are as different as possible from the pro- 

 longed screams of these animals when distressed. The 

 deep grunt of satisfaction uttered by a pig, when pleased 

 with its food, is widely different from its harsh scream 

 of pain or terror. But with the dog, as lately remarked, 

 the bark of an^er and that of iov are sounds which bv 

 no means stand in opposition to each other; and so it is 

 in some other cases. 



There is another obscure point, namely, whether the 

 sounds which are produced under various states of the 

 mind determine the shape of the mouth, or whether its 

 shape is not determined by independent causes, and the 

 sound thus modified. When vounsr infants crv thev 

 open their mouths widely, and this, no doubt, is neces- 



7 ' Theorie Physiolog'ique de la Musique,' Paris, 1868, 

 p. 146. Helmholtz has also fully discussed in this pro- 

 found work the relation of the form of the cavity of 

 the mouth to the production of vowel-sounds. 



