GENERATION OF ANIMALS, V. vii.-viii. 



The heat and cold of their place of habitation is 

 another factor contributing to the fact that the 

 natural construction of some animals is such that they 

 have deep voices, and of others, that they have high 

 voices. Breath that is hot produces deepness (heavi- 

 ness) of voice, owing to its thickness ; breath that is 

 cold produces the opposite result, owing to its thin- 

 ness. This is plain in the case of musical pipes as 

 well : people who blow comparatively hot breath 

 into the pipe — i.e., if they breathe it out as though 

 they were saying " Ah I " — play a deeper note. The 

 reason for roughness and smoothness of voice and all 

 unevenness of that sort is that the part or organ 

 through which the voice travels is rough, or smooth, 

 or, to put it generally, is even or uneven. This is 

 apparent when there is any fluid about in the trachea, 

 or if there is any roughness due to an affection : in 

 such circumstances the voice becomes uneven too. 

 FlexibiUty depends upon whether the organ is soft or 

 hard, since anything that is soft can be controlled and 

 made to assume all sorts of shapes, whereas anything 

 hard cannot. Thus this organ if it is soft can utter 

 a small sound or a large one, and therefore a high 

 one or a deep one as wejl, because it controls the 

 breath easily, as it easily becomes large or small itself. 

 Hardness on the other hand cannot (so) be controlled. 



This will be a sufficient account of those points 

 concerning the voice which we have not already 

 settled in the treatises Of Sensation and Of the Soul. 



We have already said," on the subject of the VIII 

 teeth, that their existence is not for one purpose Teeth. 

 only, nor do they exist for the same purpose in all 

 animals : some have teeth on account of nourish- 

 ment, some for self-defence and (some) for rational 



553 



