ARISTOTLE'S HOMCBOMERIA. 113 



differences, in arterial and venous blood now so called, 

 although he did not understand the causes of these differ- 

 ences. In P. ^. ii, c. 2, 6476, he points out that differences 

 in consistency, clearness, and temperature are noticeable in 

 blood taken from different parts of the same animal. Again, 

 after referring to the existence of two main blood-vessels, one 

 being the aorta and the other including the venae cavae, 

 and pointing out that these vessels are different in character, 

 he says that it is better that each should have its own blood 

 supply, and that the blood of one side of the body should be 

 distinct from that of the other.* He also says that the 

 blood in the right cavity of the heart and that of the right 

 side of the body is hotter than the rest of the blood, t 



The differences in consistency, colour, and apparent 

 purity, to which he alludes in these passages, would be 

 evident to his senses, but it is not clear how he decided that 

 there were differences of temperature, for such differences 

 as exist are very small. It is probable that his views about 

 the relative temperatures of the blood in different parts of 

 the body were dependent on his belief that the right side is 

 more honourable than the left side, the upper part than the 

 lower part, and the front than the back. 



Aristotle's statements about the coagulation of the blood 

 are numerous and interesting, but before discussing them, 

 the views of Plato, in particular, on this subject should be 

 considered, in order to ascertain to what extent Aristotle's 

 views were original. Plato, whom Aristotle does not cite, 

 says that the " fibres " cause the blood to coagulate when it 

 has been drawn from the body and allowed to cool, and that, 

 by the nature of their composition, they maintain the blood 

 at a proper degree of consistency, so that it does not become 

 liquid enough to flow through the porous structures of the 

 body, nor so sluggish as to flow with difficulty through the 

 blood-vessels. + He also speaks of serum (ix^p), and calls it 

 the watery part of the blood. § In the genuine works of 

 Hippocrates there is nothing worthy of mention on the 

 coagulation of the blood. There is an important passage in 

 the Hippocratic treatise On Flesh, § 8, which states that 

 blood coagulates on cooling, and that the " fibres" are of a 

 cold nature and glutinous. This work, however, is gene- 

 rally believed to have been written long after the time of 

 Hippocrates. 



- P. A. iii. c. 4, 6666. f Ibid. iii. c. 4, 667a. 



I Timaus, 85. § Ihid. 83. 



I 



