BOOK II. J MOTION OF EXCI1EMENT. 547 



converting them into spirit, which afterwards is exhaled, whence 

 ensues a diminution of weight, and a desiccation of which we 

 have spoken elsewhere. 1 Nor should we, in speaking of assimi 

 lation, neglect to mention the accretion which is usually dis 

 tinguished from aliment, and which is observed when mud grows 

 into a mass between stones, and is converted into a stony sub 

 stance, and the scaly substance round the teeth is converted into 

 one no less hard than the teeth themselves ; for we are of opinion 

 that there exists in all bodies a desire of assimilation, as well as 

 of uniting with homogeneous masses. Each of these powers, 

 however, is confined, although in different manners, and should 

 be diligently investigated, because they are connected with the 

 revival of old age. Lastly, it is worthy of observation, that in 

 the nine preceding motions, bodies appear to aim at the mere 

 preservation of their nature, whilst in this they attempt its 

 propagation. 



Let the twelfth motion be that of excitement, which appears 

 to be a species of the last, and is sometimes mentioned by us 

 under that name. It is, like that, a diffusive, communicative, 

 transitive, and multiplying motion ; and they agree remarkably 

 in their effect, although they differ in their mode of action, and 

 in their subject matter. The former proceeds imperiously, and 

 with authority ; it orders and compels the assimilated to be con 

 verted and changed into the assimilating body. The latter pro 

 ceeds by art, insinuation, and stealth, inviting and disposing the 

 excited towards the nature of the exciting body. The former 

 both multiplies and transforms bodies and substances ; thus a 

 greater quantity of flame, air, spirit, and flesh is formed ; but in 

 the latter, the powers only are multiplied and changed, and heat, 

 the magnetic power, and putrefaction, in the above instances, are 

 increased. Heat does not diffuse itself when heating other bodies 

 by any communication of the original heat, but only by exciting 

 the parts of the heated body to that motion which is the form of 

 heat, and of which we spoke in the first vintage of the nature of 

 heat. Heat, therefore, is excited much less rapidly and readily 

 in stone or metal than in air, on account of the inaptitude and 

 sluggishness of those bodies in acquiring that motion, so that it 

 is probable, that there may be some substances, towards the 

 centre of the earth, quite incapable of being heated, on account 

 of their density, which may deprive them of the spirit by which 

 the motion of excitement is usually commenced. Thus also the 

 magnet creates in the iron a new disposition of its parts, and a 

 conformable motion, without losing any of its virtue. So the 

 leaven of bread, yeast, rennet, and some poisons, excite and 

 invite successive and continued motion in dough, beer, cheese, of 



See the citing instances, Aphorism xL 



2x2 



