ii- 7- 35 



presence in animals is no less than the preservation of the whole 

 body. How it effects this will be seen from what follows. Some 

 writers assert that the soul is fire or some such force.''' This 

 however is but a rough and inaccurate assertion ; and it would 

 perhaps be better to say that the soul is incorporate in some 

 substance of a fiery character. The reason for this being so is 

 that of all substances there is none so suitable for ministering 

 to the operations of the soul as that which is possessed of heat. 

 For the functions of the soul are nutrition and motion, and it 

 is by heat that these are most readily effected. To say however 

 that the soul is fire is much the same thing as to confound the 

 auger or the saw with the carpenter or his craft, simply because 

 the work is wrought by the two in conjunction. So far then 

 this much is plain, that all animals must necessarily have a 

 certain amount of heat. But as all influences require to be 

 counterbalanced, so that they may be reduced to moderation and 

 brought to the mean (for in the mean, and not in either extreme, 

 lies the true and rational position), nature has contrived the brain 

 as a counterpoise to the region of the heart with its contained 

 heat, and has given it to animals to moderate the latter, com- 

 pounding it of earth and water.^ For this reason it is, that 

 every sanguineous animal has a brain ; whereas no bloodless 

 creature has such an organ, unless indeed it be, as the Poulp, 

 by analogy.^ For where there is no blood, there in consequence 

 there is but little heat. The brain then tempers the heat and 

 Seething of the heart. In order, however, that it rnay not itself 

 be absolutely without heat, but may have a moderate amount, 

 branches run from both blood-vessels, that is to say from the 

 great vessel and from what is called the aorta,"' and end in the 

 membrane which surrounds the brain ;^^ while at the same time, 

 in order to prevent any injury from the heat, these encompassing 

 vessels, instead" of being few and large, are numerous and small, 

 and their blood scanty and clear, instead of being abundant and 

 thick.^2 We can now understand why defluxions have their origin 

 in the head, and occur whenever the parts about the brain have 

 more than a due proportion of coldness. For when the nutriment 

 steams upwards through the blood-vessels, its refuse portion is 

 chilled by the influence of this region, and forms defluxions of 

 phlegm and serum. We must suppose, to compare small things 

 with great, that the like happens here as occurs in the production 

 653 a. 



