214 Biological Chemistry. 



" maltase." On hydrolysis maltose undergoes hydrolysis, 

 one molecule yielding two molecules of glucose 



C 12 H 22 11 + H 2 = 2C 6 H 12 6 (glucose) 



Lactose or milk-sugar, which occurs in milk, and is 

 readily prepared from the liquid squeezed out from the 

 clot after the milk has been clotted with rennin, is a 

 sugar confined to the animal kingdom. On hydrolysis it 

 yields a mixture of galactose and glucose 



C 12 H 22 U + H 2 = C 6 H 12 6 + C 6 H 12 6 



(Glucose) (Galactose) 



All the above disaccharoses yield characteristic osazones. 



POLYSACCHAROSES. 



The chief of these are starch and glycogen, both of 

 which yield on hydrolysis glucose. Intermediate complex 

 products, such as dextrin, are also formed. 



Starch is widely distributed throughout the animal 

 world, occurring in potatoes, and forming a large pro- 

 portion of the substance of various grains. On an in- 

 dustrial scale it is prepared chiefly from potatoes. It is 

 a very complex substance, which is insoluble in water. 

 It occurs in the form of granules, with characteristic 

 shapes which vary in the different plants. On heating 

 them with water they swell and burst, separating into an 

 insoluble cell wall which can be filtered off, and a portion 

 soluble in water and known as " soluble starch," which 

 can be precipitated from solution on the addition of 

 alcohol. The molecular weight of starch is very large ; 

 its composition is generally represented by the formula 

 7i(C 6 H 12 O 6 ) (n 1)H 2 O, and as n is very great the 

 simpler formula (C 6 H 10 O 6 ) n is sufficiently accurate. The 

 more complex formula will explain the hydrolysis by acids 

 of one molecule of starch into n molecules of glucose. 



