PARTS OF ANIMALS, II. vii. 



holding their heads upright. These matters have 

 been spoken of separately in the treatises on Sensation 

 and on Sleep.'* 



I said the brain is compounded of Water and 

 Earth. This is sho^v■n by Avhat happens when it is 

 boiled. Then it becomes solid and hard : the earthy 

 substance is left behind after the Water has evapor- 

 ated oAving to the heat. It is just Avhat happens 

 when pulse and other forms of fruit are boiled ; they 

 also get hard and earthy altogether, because the 

 greater part of them is earth, and the fluid mixed 

 Avith it departs when they are boiled. 



Of all the animals, man has the largest brain for 

 his size ; and men have a larger brain than \vomen. ^ 

 In both cases the largeness is due to there being a 

 great deal of heat and blood in the region around the 

 heart and the lung. This too explains why man is 

 the only animal that stands upright. As the hot sub- 

 stance prevails in the body it induces growth, begin- 

 ning from the centre along its ολ^τι line of travel. 

 It is against great heat, then, that a large supply of 

 fluid and cold is provided. This bulk of moisture 

 is also the reason why the bone that surrounds the 

 brain (called by some the bregma) ^ is the last of all 

 to solidify ; the hot substance takes a long time to 

 evaporate it off. This phenomenon does not occur 

 in any other of the blooded animals. Again, man 

 has more sutures in the skull than any other animal, 

 and males have more than females. The size of the 

 brain is the reason for this also ; it is to secure 

 ventilation, and the larger the brain, the more 

 ventilation it requires. If the brain becomes unduly 

 fluid or unduly solid, it \vill not perform its proper 

 function, but will either fail to cool the blood or else 



Γ 155 



