44 INTRODUCTION TO GENERAL PHYSIOLOGY 



of this hydroxyl then becoming transferred to the aldehyde group. 

 Thus : 



H C^ OH 



H C OFT 



I >0 



H C OH 



I 

 H C 



H C OH 



H C OH 

 H 



Changes of this kind are common in organic chemistry. If we 

 designate the neighbouring carbon to the aldehyde by the prefix a, 

 that one united to the aldehyde in our formula will be y, and the 

 compound is a y lactone, being of the nature of an internal 

 anhydride. 



Next, if we transfer the two hydrogens from the a-carbon to the 

 aldehyde group, we have another kind of sugar which has an 

 alcohol group at both ends and a CO next to it at one end. Thus : 



H 

 HCOH 



CO 



HCOH 

 HCOH 

 HCOH 

 HCOH 



H 



CO is the characteristic group of the ketones, and the sugar in 

 question is called a " ketose." It is known as " fructose," and 

 exists, combined with glucose, in cane sugar. 



The student should never forget that the representation of 

 chemical compounds in the way that we have done is a conventional 

 diagram of the facts shown by the properties of these compounds 

 with regard to the particular constituent atoms which are united to 

 each other. For one thing, we are compelled to write them on a 

 plane surface, whereas, of course, they are solids, with three 

 dimensions in space. The " bonds," again, are not hooks, or 

 similar rigid attachments, but forces, probably of electrical nature. 

 Further, there is every reason to believe that an element in a 

 particular kind of combination is not the same thing as it is in 

 another kind of combination, or when free, although the change from 



