BOOK XI. xci. 225-xciv. 228 



blood retreats and is novvhere to be found, and that 

 many creatures do not shed blood when stabbed, which 

 happens only to a human being. For those which we 

 have spoken of° as changing their colour really 

 assume the colour of some other object by a sort of 

 reflexion ; only man actually changes colour in 

 himself. All diseases and death reduce the amount 

 of blood. 



XCII. There are persons who think that subtlety Psycho- 

 of mind is not due to thinness of the blood, but that ^^y^'^ "^^ 

 animals are more or less brutish owing to their skin 

 and bodily coverings, as for instance molhiscs and tor- 

 toises ; and that the hides of oxen and bristles of pigs 

 obstruct the thinness of the air when being inhaled, 

 and it is not transmitted pure and Uquid ; so also in 

 man, when his skin being thicker or more callous 

 shuts it out — ^just as if crocodiles did not possess both 

 a hard hide and cunning. XCIII. The skin of the 

 hippopotamus is so thick that it is used for the points 

 of spears, and yet its mind possesses a certain medical 

 abiUty.* The hides of elephants also supply im- 

 penetrable bucklers (though nevertheless they are 

 credited with the most outstanding mental subtlety 

 of all quadrupeds) ; and consequently their skin itself 

 is devoid of sensation, especially in the head. It 

 does not heal up when wounded in any place where 

 there is only skin and no flesh, as in the cheek and 

 eyelid. 



XCIV. Viviparous species have bristles, but ovi- Bristies, 

 parous ones have feathers or scales, or shells Uke scaies. 

 tortoises, or bare sldn Uke snakes. Feathers in aU 

 cases have hoUow stalks ; when cut off they do not 

 grow again, but when plucked out others grow in 

 their place. Insects use fragile membranes to fly 



575 



