ARISTOTLE. 31 



In the work " On the Parts of Animals," the author 

 considers not only the phenomena of life exhibited by each 

 species, but also the cause or causes to which these 

 phenomena are attributable. After a general introduc- 

 tion, he proceeds to enumerate the three degrees of 

 composition, viz. : 



(1) " Composition out of what some call the elements, 



such as air, earth, water, and fire," or " out of 

 the elementary forces, hot and cold, solid and 

 fluid, which form the material of all compound 

 substances." 



(2) Composition out of these primary substances of 



the homogeneous parts of animals, e.g. blood, 

 fat, marrow, brain, flesh, and bone. 



(3) Composition into the heterogeneous parts or 



organs. These parts he describes in detail, 

 considering those belonging to sanguineous 

 animals first and most fully. 



These divisions correspond roughly to the threefold 

 study of structure which we nowadays recognize as 

 chemical, histological, and anatomical. 



As examples of Aristotle's method of treatment, his 

 descriptions of blood, the brain, the heart, and the lung 

 may be considered. 



Of the blood he says, " What are called fibres are 

 found in the blood of some animals, but not of all. 

 There are none, for instance, in the blood of deer and 



