MONOSACCHARIDES IN LIVING TISSUES 7l 



content of the food and may occur when the combustion of carbo- 

 hydrates in the tissues would appear to be otherwise normal. 



The pentoses are widely distributed in the vegetable kingdom, 

 chiefly in the form of polysaccharides, bearing the same relation to the 

 pentoses as starch and glycogen do to the hexoses. These polysac- 

 charides, which are complex anhydrides of the monosaccharides, are 

 known as Pentosans. The following table shows the percentage of 

 pentosan, in terms of pentose, found in the dry substance of various 

 vegetable foods: 



Meadow hay . , . . . . . '. . . . . ... . . . 21.64 



Rape cake . .... 11.50 



Oil-seed cake ...>.... . 9.07 



Bruised barley . . . . . . . . . . . .... 7.96 



Rice flour ;...-. .. : . . . 5.73 



Sesame cake . . . ,. . . . . 3.87 



Table turnip . ., . . .'...'. . . . 1.13 



Spinach . . . . . ^ 1.02 



With regard to the distribution of the hexoses; Levulose is not 

 often found in the animal kingdom. In honey it occurs together with 

 glucose and is immediately derived from the juices of flowers, but it is 

 a question whether it is ever normally found in animal tissues. It is 

 occasionally found in the urine, and is then derived directly from the 

 levulose absorbed from the intestine; it may be regarded as a sign 

 either of excessive overindulgence in sweets or honey or else, if this 

 origin can be excluded, as a sign of overactivity of the pituitary gland, 

 which as we shall see later on, lowers the limit of tolerance for all forms 

 of sugar. A urine which yields evidence of the' presence of a reducing 

 sugar should therefore always be tested for levulose by Selivanoff's 

 test (see p. 62) before a provisional diagnosis of diabetes is decided 

 upon. 



In vegetable tissues levulose is widely distributed, especially com- 

 bined with glucose to form cane-sugar. It is also found in the form 

 of a complex anhydride, or polysaccharide, Inulin in the tubers of 

 dahlias and in the sweet potato. 



Grape-sugar, or d-glucose, is the most important of all the mono- 

 saccharides in the animal economy. It is the central figure in the 

 carbohydrate metabolism. Polysaccharides are broken down to 

 glucose before assimilation, and again before utilization as a source 

 of energy, or transportation from one part of the body to another. It 

 is the circulating form of carbohydrate, Glycogen and other poly- 

 saccharides being the storage-forms. In view of these facts the 

 absurdity will be apparent of the effort which was made in certain 

 circles in the United States, a few years ago, to represent glucose and 

 glucose-syrups as deleterious articles of food. Provided they contain 

 no other 'constituents which are harmful such preparations are merely 

 solutions of the only carbohydrate which is to any important extent 

 a normal and invariable constituent of the blood. 



