The Carbohydrates and Their 

 Metabolism 



A. I. EIISTGER 



AND 



EMIL J. BAUMANN 



NEW YORK 



1. Introduction 



The carbohydrates, or sugars as they are called, are found in all cells. 

 The name sugar is commonly applied to anything having a sweet taste, as 

 sugar of lead for lead acetate. It is now used non-technically for some 

 of the simpler members of this group milk sugar (lactose), cane sugar 

 (sucrose), etc. The generic name carbohydrate is derived from the fact 

 that these substances are composed of the elements carbon, hydrogen and 

 oxygen, the latter two being in the proportion in which they exist in 

 water two atoms of hydrogen to one of oxygen in most, though not all 

 cases ; in other words, they are hydrates of carbon or carbohydrates. 



In the plant world the carbohydrates are found serving two main 

 functions : first, they act as the main constituent of supporting tissues or 

 framework of the cell cellulose ; second, reserve food is stored up in this 

 form as starches. In the animal world, carbohydrates no longer act as 

 supporting structures of cells. Nitrogenous substances, belonging mainly 

 to the class called proteins, take the place of them, but they are found 

 as a form of reserve food glycogen or animal starch. It is interesting 

 to note that in some of the lower animal forms (in some molluscs), the 

 supporting tissue, chitin, is a substance that may be considered as an 

 intermediate of the proteins and carbohydrates. It is a nitrogenous carbo- 

 hydrate from which glucosamine can readily be obtained. Carbohydrates 

 are also found in the nuclei of all cells, in nucleic acids, and one of 

 the simplest sugars, glucose, is almost always present in tissue fluids. 

 They are the simplest organic substances found in living matter and the 

 most abundant. All the more complex constituents of cells are derived 

 from them ultimately. 



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