PARTS OF ANIMALS, II. i. 



It is possible for the non-uniform parts to be con- 

 structed out of the uniform substances, either out of 

 many of them, or out of one only. (Examples of the 

 latter are furnished by certain of the viscera, which, 

 although they are of manifold shapes and forms, 

 yet for all practical purposes may be said to consist 

 of one only of the uniform substances.) But it is 

 impossible for the uniform substances to be con- 

 structed out of the non-uniform parts : for then 

 we should have an uniform substance consisting of 

 several non-uniform parts, which is absurd. 



These, then, are the Causes o\Wng to which some of 

 the parts of animals are simple and uniform ; while 

 others are composite and non-uniform. 



Now the parts can also be divided up into (a) 

 instrumental parts and (6) sense-organs.'* And we 

 may say that each of the instrumental parts of the 

 body, as I have stated earlier, is always non-uniform, 

 while sensation in all cases takes place in parts that 

 are uniform. The reasons why this is so are the 

 follo\Wng : The function of each of the senses is 

 concerned w-iih a single kind of sensible objects ; and 

 the sense-organ in each case must be such as can 

 apprehend those objects. Now when one thing 

 affects another, the thing which is affected must be 

 potentially/ what the other is actually ; so both are the 

 same in kind, and therefore if the affecting thing is 

 single, the affected one is single too. Hence we 

 find that while with regard to the parts of the 

 body such as hand, or face, none of the physiologers 

 attempts to say that one of them is earth, and 

 another water, and another fire ; yet they do conjoin 



" organ " in the stricter meaning of the word. " Organs " 

 are normally " non-uniform," sense-organs are " uniform." 



113 



