38 PHYSIOLOGICAL CHEMISTRY 



EXPERIMENTS ON XYLOSE 

 1-4. Same as for arabinose (see above). 



RHAMNOSE, C 6 H 12 6 



Rhamnose or methyl-pentose is an example of a true carbohydrate 

 which does not have the H and atoms present in the proportion to 

 form water. Its formula is CeH^Os. It has been found that rham- 

 nose when ingested by rabbits or hens has a positive influence upon the 

 formation of glycogen in those organisms. 



DISACCHARIDES, C 12 H 22 On 



The disaccharides as a class may be divided into two rather dis- 

 tinct groups. The first group would include those disaccharides which 

 are found in nature as such, e.g., sucrose and lactose, and the second 

 group would include those disaccharides formed in the hydrolysis of 

 more complex carbohydrates, e.g., maltose and iso-maltose. 



The disaccharides have the general formula Ci 2 H 22 On, to which, 

 in the process of hydrolysis, a molecule of water is added causing the 

 single disaccharide molecule to split into two monosaccharide (hexose) 

 molecules. The products of the hydrolysis of the more common di- 

 saccharides are as follows: 



Maltose = glucose + glucose. 



Lactose = glucose + galactose. 



Sucrose = glucose + fructose. 



All of the more common disaccharides except sucrose have the power 

 of reducing certain metallic oxides in alkaline solution, notably those 

 of copper and bismuth. This reducing power is due to the presence 

 of the aldehyde group ( CHO) in the sugar molecule. 



MALTOSE, Ci 2 H 22 O u 



Maltose or malt sugar is formed in the hydrolysis of starch through 

 the action of an enzyme, vegetable amylase (diastase) , contained in sprout- 

 ing barley or malt. Certain enzymes in the saliva and in the pancreatic 

 juice may also cause a similar hydrolysis. Maltose is also an intermedi- 

 ate product of the action of dilute mineral acids upon starch. It is 

 strongly dextro-rotatory, reduces metallic oxides in alkaline solution 

 and is fermentable by yeast after being inverted (see Polysaccharides, 

 page 42) by the enzyme maltase of the yeast. In common with the other 

 disaccharides, maltose may be hydrolyzed with the formation of two 

 molecules of monosaccharide. In this instance the products are two 

 molecules of glucose. With phenylhydrazine maltose forms an osa- 

 zone ; maltosazone. The following formula represents the probable 

 structure of maltose: 



