MOVEMENT OF ANIMALS, vii.-viii. 



iron," while the sinews correspond to the strings, the 

 setting free and loosening of which causes the move- 

 ment. In the marionettes and the toy-carriages no 

 alteration takes place, though, if the inner wheels 

 were to become smaller and then again larger, the 

 same circular movement would take place. In the 

 animal, however, the same part can become both 

 greater and smaller and change its form, the mem- 

 bers increasing through heat and contracting again 

 through cold and thus altering. Alteration is 

 caused by imagination and sensations and thoughts. 

 For sensations are from the first a kind of altera- 

 tion, and imagination and thought have the effect 

 of the objects which they present ; for in a Avay the 

 idea conceived — of hot or cold or pleasant or terrible — 

 is really of the same kind as an object possessing one 

 of these qualities, and so we shudder and feel fear 

 simply by conceiving an idea ; and all these affec- 

 tions are alterations, and when an alteration takes 

 place in the body some parts become larger, others 

 smaller. Now it is clear that a small change taking 

 place in an origin of movement ^ causes great and 

 numerous changes at a distance ; just as, if the rudder 

 of a boat is moved to an infinitesimal extent, the 

 change resulting in the position of the boAvs is con- 

 siderable. Furthermore, when, owing to heat or 

 cold or a similar affection, an alteration is caused 

 in the region of the heart — and even in an imper- 

 ceptibly small part of it — it gives rise to a consider- 

 able change in the body, causing blushing or pallor 

 or shuddering or trembling or the opposites of these. 

 VIII. The origin, then, of movement, as has already 



* i.e. here, the heart, cf. below, 701 b 30 ; see also note on 

 698 bl. 



465 



