62 THE HISTOliY OF ANIMALS. [u. III. 



and are more like spines, as in the hedgehog, wherein they 

 resemble nails. So again the nails in some animals are not 

 different from bones in point of hardness. 



4- Man has the thinnest skin in proportion to his size. 

 There is a mucous, glutinous fluid in the skin of all animals, 

 less in some, more in others, as in the skins of oxen, from 

 which glue is made ; and sometimes glue is made from fishes. 

 "When the skin alone is cut it is insensible, especially 

 that upon the head, from the absence of flesh between that 

 and the bone. Wherever the skin is without flesh it does 

 not unite again after being cut, as the thin part of the 

 cheek, the prepuce, and the eyelid. In all animals the skin 

 is continuous, and it is only wanting in places where there 

 are natural passages for exudation, and at the mouth 

 and nails. All sanguineous animals have a skin: all, 

 however, have not hair, but those which are described 

 above. 



5. The colour of the hair changes in men as they grow 

 old, and the hair becomes grey. This takes place in other 

 animals, but not so remarkably as in the horse. The hair 

 begins to grow white from the extremity. Most white 

 animals are white from their birth, wherefore it is plain 

 that whiteness does not arise from dryness, as some persons 

 suppose, for no animal is born dry. In the exanthematous 

 disease, called whiteness, all the hair becomes hoary ; and 

 some patients, who have suffered from illness, after the hair 

 has fallen off on recovery, have regained their dark-coloured 

 hair. Hair which is covered up becomes white more 

 readily than that which is exposed to the air ; in man the 

 temples are the first to grow grey, and the fore part of 

 the head before the hind part, and last of all the hair on 

 the pubes. 



6. Some of the hair exists on the body at the period 

 of birth, and some appears afterwards. In man alone the 

 hair on the head, eyelashes, and eyebrows exist at birth. 

 The hair on the pubes, in the armpits, and on the chin ap- 

 pear successively after birth, so that the parts on which 

 the hair appears at birth, and those on which it grows after- 

 wards are the same in number. In old age the hair on the 

 head especially is the first to fail, and falls off. This is 

 only in front, for no one ever becomes bald on the back 



