40 LECTURE III. 



does not decompose into maltose alone, but quite a number of other prod- 

 ucts are formed at the same time. The whole process of dissolving the 

 starch by the action of diastase has been made the subject of countless 

 studies. A large number of intermediate products have been isolated 

 and provided with special names, but it would be out of place to discuss 

 here all the transformation products that have been described, for their 

 manner of formation and their chemical characteristics are not yet accu- 

 rately known. The reason for this is mainly that we are in doubt con- 

 cerning the homogeneity of the starting material, the starch itself, and 

 know still less concerning diastase. 



Ferments, corresponding in their action to this malt-diastase, are widely 

 distributed in nature, and take an important part in the metabolism of 

 carbohydrates in plants. They give back to the metabolism of the plant 

 its reserve-stores, the insoluble starch. 



The animal organism, as well, is known to contain ferments which dis- 

 solve starch and convert it into sugars, and in this process maltose is 

 formed as an intermediate product, which then breaks down into two 

 molecules of grape-sugar. Later on we shall have to consider such trans- 

 formations in detail. It may be mentioned here, however, that in the 

 breaking down of glycogen, the stored carbohydrate of the animal system, 

 maltose has also been observed. 



Polysaccharides which are anhydrides of three and four sugar molecules 

 are also known and have been accurately described, while in the case of the 

 more complicated compound sugars we know nothing at present concern- 

 ing the number of sugar molecules which take part in their formation. 

 We know of a trisaccharide, rhamninose, which is composed of two pentoses 

 and one hexose; this is obtained in the decomposition of a glucoside 

 obtained in the fruit of Rhamnus infectoria, the xanthorhamnin. Rham- 

 ninose breaks down into two molecules of rhamnose and one molecule of 

 d-glucose. Trisaccharides composed of three molecules of hexose are 

 more widely distributed in nature. Of these we will mention raffinose 

 (also known as melitriose or gossypose) which is found in different plants 

 and in the sugar-beet. A tetrasaccharide, stachyose, (manna-tetrasac- 

 charide), is known, and was first obtained from the manna of ash. On 

 being treated with dilute mineral acids it takes on water, and is decom- 

 posed into one molecule of d-fructose, one of d-glucose, and two of 

 d-galactose. 



The higher polysaccharides have been studied but little. We know 

 merely that the complete hydrolysis of these compounds gives mono- 

 saccharides as final products. We know nothing, however, concerning 

 the number of molecules of simple sugar which take part in their forma- 

 tion. To the widely different substances of this large group the general 

 formula (CeHio05)a; is given, which signifies that the compound is com- 



