CARBOHYDRATES AXD RELATED BODIES. 47 



some of the solution with dilute hydrochloric acid ten minutes; neutralize 

 the acid nearly, cool and again test with iodine. No color is now pro- 

 duced, as glycogen has disappeared under the treatment, having been con- 

 verted into sugar. 



It has been remarked above that after death the store of glycogen in 

 the liver rapidly disappears, so that tests applied at the end of a day or 

 two fail to show its presence. This may be shown as follows : 



Ex. Cut some common beef liver from the market into small bits and 

 extract with boiling water. Boil longer to coagulate protein bodies, after 

 adding some sodium sulphate. Apply the iodine test for glycogen, which 

 is found absent, and the Fehling test for sugar, which is found present in 

 quantity. It is an excellent exercise also to determine the amount of sugar 

 which may be obtained from a given weight of liver. In this test the 

 extraction must be repeated with several portions of water. 



The Gums. Some of these occur in nature as products 

 related to the pentose group of sugars referred to some pages 

 back. Others are related to starch and on transformation 

 yield finally hexoses. The group of gums includes further 

 the dextrin bodies formed from starch by several reactions, 

 one of which has been already illustrated. The transforma- 

 tion of starch by the action of weak acids or enzymes is far 

 from being a simple process and much uncertainty still exists 

 as to the number of intermediate products between the parent 

 substance and the final maltose or glucose. Some writers 

 have attempted to distinguish several well defined stages in 

 the reaction and describe as definite bodies erythrodextrin, 

 achroodextrin, amylodcxtrin and maltodextrin. The first 

 gives a violet-red color with iodine and is easily precipitated 

 by alcohol; the second gives no color with iodine, but is 

 still precipitated by alcohol. It shows reducing power with 

 Fehling's solution, and may be looked upon as one of the end 

 products of the action of diastase on starch, maltose being the 

 other. The name amylodextrin is given to a product of dias- 

 tatic action and also to a dextrin formed by the treatment of 

 starch with very dilute acids. It is said to show a purple 

 color with iodine, and to exhibit very strong dextro rotation. 

 The existence of malto-dextrin is affirmed by several writers, 

 but the properties of the substance are not well established. 



