PARTS OF ANIMALS, II. iii.-iv. 



creatures. This explains why the blood diminishes 

 in quantity when no food is taken and increases 

 when it is ; and why, when the food is good, the 

 blood is healthy, when bad, poor. These and 

 similar considerations make it clear that the purpose 

 of the blood in living creatures is to provide them 

 with nourishment ; and also why it is that when the 

 blood is touched it yields no sensation, as flesh does 

 when it is touched. Indeed, none of the residues 

 yields any sensation either, nor does the nourishment. 

 This difference of behaviour is because the blood is 

 not continuous with the flesh nor conjoined to it 

 organically : it just stands in the heart and in the 

 blood-vessels like water in a jar. A description of 

 the way in which the parts of the body derive their 

 growth from the blood, and the discussion of nourish- 

 ment in general, comes more appropriately in the 

 treatise on Generation " and elsewhere. For the 

 present it is enough to have said that the purpose 

 of the blood is to provide nourishment, that is to 

 say, nourishment for the parts of the body. So 

 much and no more is pertinent to our present 

 inquiry. 



IV. The blood of some animals contains what are The uniform 

 called fibres ; the blood of others (e.g. the deer and B^iood! 

 the gazelle) does not. Blood which lacks fibres does 

 not congeal, for the following reason. Part of the 

 blood is of a more watery nature, and therefore 

 does not congeal ; while the other part, which is 

 earthy, congeals as the fluid part evaporates off. 

 The fibres are this earthy part. 



Now some of the animals whose blood is watery 

 have a specially subtle intelligence.^ This is due not 

 to the coldness of their blood, but to its greater thin- 



