CHEMICAL CHARACTERS OF CELL 43 



organism which produced them. . . . We may, 

 therefore, sum up in regard to the living crystals ^ 

 as follows their composition is that of calcite 

 crystals, but their external form is that which the 

 sponge requires, and not that which they would 

 naturally assume. They furnish us, in fact, with 

 a beautiful instance of what is called adaptation ; 

 that is to say, the fact that any living organism 

 tends to have just that form, structure and organ- 

 isation in all its parts which it requires in order to 

 maintain its existence in its peculiar mode of life, 

 whatever it may be." 1 J & 



Finally, as regards the question of crystallisa- V 

 tion, the crystal of any rock can be dissolved and 

 will re-crystallise under suitable conditions, and \ 

 these two processes can be repeated ad infinitum. I 

 But the living cell once destroyed cannot be 

 reformed, another fundamental difference between \ 

 the two. 



The question of bye-products is one which has Bye-pro- 

 been already touched upon more than once ; and 

 what a remarkable series of bye-products there 

 are when one contemplates the vegetable world 

 alone ! There are the numerous alkaloids and 

 essential oils which are so much used in medicine 

 and in the arts, the essences with which perfumes 

 are made, waxes, turpentines and a whole host of 

 other compounds all constructed by the cell in its 



