Animals Before Man 



having been retained, although the original 

 material of which it was composed has been 

 replaced by silica, or flint, as it is more famil- 

 iarly called. 



Since these changes require certain favora- 

 ble conditions and take place very slowly, only 

 objects that retain their shape for a considera- 

 ble time can be thus altered ; so, flesh can never 

 be turned into stone, and consequently there is 

 no such thing as a " petrified body." 



The familiar experiment of soaking a bone 

 in weak muriatic acid shows how much animal 

 matter there is in a skeleton ; and it will sur- 

 prise any one who will try a tooth that of a 

 horse, for example in place of a bone, to find 

 how much of this, too, is made up of gristle-like 

 material. There is so much of this in the tusks 

 of elephants or teeth of sperm whales that they 

 can be made into gelatin, and this might be 

 used for making elephant or whale jelly. This 

 is the reason why the tusks of ancient elephants 

 are so rarely found ; the soft material of the 

 tusks washed out so much more rapidly than 

 mineral substances filtered in to replace it, 



10 



