V] CARBOHYDRATES 75 



excess. Filter again and the filtrate will contain the sugars. Boil the latter and add 

 Fehling's solution drop by drop till reduction ceases. Filter off the copper oxide and 

 then boil the solution with dilute sulphuric acid for a few minutes and make neutral 

 to litmus. Reduction will occur on adding more Fehling and boiling, owing to the 

 inversion of the cane-sugar present. 



Expt. 76. To show the presence of hexoses in the leafhy means of the formation of 

 glucosazone. Leaves of Beta, Chaerophyllum sylvestre, or Tropaeolum may be used. 

 Extract as in the previous experiment and precipitate the glucosides with the minimal 

 amount of basic lead acetate. Test for osazone in the filtrate as in Expt. 41 {d). 



Expt. 11. To obtain starch from green leaves. Weigh out 25 gms. of leaflets of the 

 Pea {Pisum sativum). The leaves should have been picked in the evening after a 

 sunny day, and it does not matter if the cut leaves are left overnight. Dip the leaf- 

 lets for a moment into boiling water, remove excess of water and drop them into 

 200 c.c. of 96-98% alcohol and boil till the chlorophyll is extracted: then filter. 

 Take the residue of leaves and pound (but not finely) in a mortar and then wash 

 thoroughly with distilled water. Filter through muslin and press free from water 

 (this process extracts most of the protein). Boil the residue with 100 c.c. of water and 

 filter. To the filtrate add iodine. At first the colour may disappear owing to the 

 presence of protein in solution in addition to the starch. When more iodine is added 

 a deep blue coloration is formed. 



Plant Enzymes which hydrolyze Carbohydrates. 



Diastase. In the plant starch may be regarded as a reserve product. 

 It is synthesized from sugar, and may be again hydrolyzed into sugar. 

 It can be shown experimentally that starch is converted into glucose by 

 boiling with acids, but in the plant the hydrolysis of starch is catalyzed 

 by the enzyme, diastase. Although the reaction is doubtless of con- 

 siderable complexity, it may, broadly speaking, be represented as 

 follows: 



(C6Hio05)„-}-H20 >■ (C6Hio05)a; + Ci2H220ii 



Dextrin Maltose 



Thus the final products under these conditions are dextrin and the 

 disaccharide, maltose; and not glucose. 



It is reasonable to assume that cells which contain starch also either 

 contain, or are capable of producing, diastase. But the amount of 

 diastase present, or at any rate capable of being extracted, varies in 

 different tissues. Diastase, like most enzymes, is soluble in water. In 

 many cases, however, a water-extract from fresh crushed tissues in which 

 diastase occurs, will not contain any appreciable amount of enzyme. 

 This is sometimes due to the fact that the protoplasm does not readily 

 yield up the enzyme until it has been killed. If the tissues are dried at 

 a moderate temperature (30-40° C.) both the powdered leaves them- 

 selves and a water extract are fairly rich in diastase ; or, if the living 



