THE PHILOSOPHY OF BIEDS' NESTS. 213 



the absence of any sufficiently powerful stimulus to 

 change or improvement. No one imagines that if an 

 infant Arab could be transferred to Patagonia or to 

 the Highlands, it would, when it grew up, astonish 

 its foster-parents by constructing a tent of skins. On 

 the other hand, it is quite clear that physical condi- 

 tions, combined with the degree of civilization arrived 

 at, almost necessitate certain types of structure. The 

 turf, or stones, or snow the palm-leaves, bamboo, or 

 branches, which are the materials of houses in various 

 countries, are used because nothing else is so readily 

 to be obtained. The Egyptian peasant has none of 

 these, not even wood. What, then, can he use but 

 mud ? In tropical forest-countries, the bamboo and the 

 broad palm-leaves are the natural material for houses, 

 and the form and mode of structure will be decided 

 in part by the nature of the country, whether hot or 

 cool, whether swampy or dry, whether rocky or plain, 

 whether frequented by wild beasts, or whether subject 

 to the attacks of enemies. When once a particular 

 mode of building has been adopted, and has become 

 confirmed by habit and by hereditary custom, it will 

 be long retained, even when its utility has been lost 

 through changed conditions, or through migration into 

 a very different region. As a general rule, through- 

 out the whole continent of America, native houses are 

 built directly upon the ground strength and security 

 being given by thickening the low walls and the roof. 

 In almost the whole of the Malay Islands, on the 

 contrary, the houses are raised on posts, often to a 



