92 CONSTITUENTS OF ANIMALS, 



acts more strongly on the tin, which cannot act strongly on 

 the copper.* Again, if water be deprived of its hydrogen, 

 a gas is left having properties very different from those of 

 water. On Aristotle s assumption, this should be explained 

 by saying that the water had been changed by an addition 

 of the element air, whereas hydrogen, which would be of 

 the nature of Aristotle s element air, has been taken away. 

 He was also quite unaware that the physical properties of a 

 substance may be changed while its composition remains 

 the same. 



Eespecting the physical constitution of matter, Aristotle 

 held that matter was continuous and not made up of indi 

 visible parts.! He rejected the atomic theories of Leucippus, 

 Democritus, and other ancient Greek philosophers who 

 considered matter to consist of atoms or small indivisible 

 particles separated by interspaces and in a state of motion. 

 This theory has only a superficial resemblance to the modern 

 atomic theory of chemists, and was open to the objection 

 that it did not satisfactorily explain how the atoms were 

 held together. Aristotle s theory that matter was continuous 

 was at least not open to this objection. Compared with the 

 theories of the ancient atomists, it might be said that, 

 broadly speaking, matter was considered by Aristotle to be 

 vitreous or colloidal, and by the atomists to be granular. 

 The modern theory takes account of the action of chemical 

 and physical forces which were quite unknown both to the 

 atomists and to Aristotle. 



The substances, or homoeomeria, resulting from the 

 combination or mixis of the elements earth, water, air, 

 and fire, will next be considered. According to Aristotle, a 

 part of a homoeomerion, such as flesh, may be correctly 

 called by the name given to the homoeomerion itself, but a 

 part of an anhomoeomerion, such as a hand, cannot be 

 properly designated by the name of the anhomoeomerion .J 

 He gives numerous examples of his homoeomeria, such as, 

 for example, flesh, blood, splanchnon or vascular material 

 forming the liver and other chief viscera, fat, marrow, milk, 

 bile, tendon, cartilage, bone, wood, stone, bronze, gold, silver, 

 and other metals. These examples show that Aristotle s 



* DC Gener. et Corr. L c. 10, 3286. 

 f Physics, iii. cc. and 7. 



I H. A. i. c. 1, s. 1 ; P. A. ii. c. 2, 6476, ii. c. 9, 6556 ; De Gener. et 

 Corr. i. c. 1, 314a. 



