222 THE FITNESS OF THE ENVIRONMENT 



high temperatures without undergoing chem- 

 ical change, but there are hardly any organic 

 substances which can survive such treatment. 

 Organic substances are also peculiarly liable 

 to modification from the action of light and 

 air. These are, however, but rough indica- 

 tions of instability, and a special case will help 

 more clearly to define the real characteristic. 



THE SUGARS 



In accordance with the researches of Emil 

 Fischer, the following constitution is ordina- 

 rily assigned to glucose. 1 



H 



I 



C = 



I 

 H-C-O-H 



I 

 H-O-C-H 



I 

 H-C-O-H 



I 

 H-C-O-H 



CH 2 OH 



1 A discussion of this formula may be found in any text- 

 book of organic chemistry. 



