74 Intracelliilar Carbohydrates [Sept. 



Starch is the most important storage carbohydrate in plants. 

 Glycogen plays a similar part in animals. Glycogen occurs most 

 conspicuously in the liver, in smaller proportions in muscles, but to 

 some extent in all animal cells and organs. 



The blood receives a steady supply of glucose from the alimen- 

 tary tract yet the glucose content of the blood is practically con- 

 stant. The glucose in the blood readily enters the body cells and 

 supplies them with calorific material and substance for advantageous 

 coordinations and constructions. Maltose may also be mentioned 

 as another free sugar in animal cells, but it exists only in traces, 

 probably arising from glycogen. Lactose is conspicuous in mam- 

 mary cells during lactation. 



Combined carbohydrates. Besides the carbohydrates which are 

 free in the plant cell there are other important substances which 

 contain the sugar groups in combined condition. The glucosides 

 are noteworthy examples of this type. Glucosides consist, in most 

 cases, of sugar (hexose) united with another substance, usually of 

 the carbocyclic series. Glucosides are often held in their own spe- 

 cial cells in storage until a rupture of the cells occurs, then the 

 hydrolytic enzymes of neighboring cells attack and rapidly resolve 

 the glucosides into their sugars and cyclic constituents. The 

 sugars in glucosidal substances act as a reserve supply of carbohy- 

 drate and the associated part is often an easily oxidizable material, 

 or one having a striking odor, peculiar color, antiseptic properties 

 and so on. The role of the glucosides in the plant is not known, but 

 the widely diverse nature of their component parts makes it likely 

 that the latter are important factors in the plant's life processes. 

 The nudeoproteins comprise another large class of combined car- 

 bohydrates, and contain hexose or pentose radicals. The origin 

 of the nudeoproteins in the cell nucleus indicates that they are inti- 

 mately involved in the phenomena of heredity. Practically all 

 plant lecithans already prepared have contained considerable 

 amounts of reducing sugars, mostly hexoses. Whether such sugars 

 are constituent parts of lecithan molecules, or merely accidental 

 impurities in the products, cannot be said with certainty at present. 



Among the combined carbohydrates of animal cells nudeopro- 

 teins may be mentioned as being important in many ways, as has 



