86 J on Dial of Agriculture. [8 Feb., 1907, 



to a small extent, in barley and beet. When boiled with an acid it gives 

 rise to a mixture of dextrose, levulose and galactose. 



A number of compound sugars mth more than three components is 

 known, but as these are of little bio-chemical importance we may pass to 

 the carbohydrates with many components. 



POLYSACCHARIDES. — These carbohydrates are each compounded 

 of a larce number of sugar components, how large it is as vet im}x>ssible 

 to say. The polysaccharides differ markedly from the sugars of which thev 

 are composed ; they are not sweet to the taste, they do not ferment with 

 veast, they do not give the copper sulphate reaction, many are in.soluble in 

 water, and only a verv few can be obtained crystalline. When boiled with 

 an acid a polysaccharide breaks up into its sugar components, in some cases 

 readily, in some cases with great difficulty. 



1. Starch. — Of the wide distribution of this carbohydrate in the vege- 

 table kingdom and its importance in animal nutrition little need here be 

 said. Starch occurs in nature in the form of microscopic grains which 

 vary in size and shape according to the plant from which they are derived. 

 It is insoluble in cold water, but soluble in hot, forming a paste which sets 

 into a jelly on cooling. When treated with a solution of iodine it gives a 

 rich blue colour, a reaction which can be used as an analytical test. When 

 boiled with an acid it passes through a number of transition stages, includ- 

 ing the dextrins and maltose, and is finally transformed into dextrose. 

 When acted upon by the ferment diastase it passes through the dextrin 

 stages, but ends as maltose, as has already been noted. Though important 

 as an animal food, starch is not found anyAvhere in the animal body. 



2. Dextrins. — These bodies represent steps in the splitting up of 

 starch under the influence of acids or a ferment. They are all soluble in 

 cold water, and give nO' colour with iodine, except the highest members of 

 the series which give a chestnut tint. 



3. Glycogen, also called Animal Starch. — This polysaccharide rather 

 resembles the higher dextrins than starch. It is soluble in water, and gives 

 an intense chestnut brown colour on treatment with iodine. Diastase 

 transforms it into maltose, but acids can carry it further, like starch and 

 the dextrins, into dextrose. It is found in the liver and in muscle tissue 

 and in manv li\ing cells. It functions as a store of. fuel food on which the 

 body can draw at need, just as starch, and to some extent the celluloses act 

 as reserve material in the plant kingdom. 



4. Cellulose. — This substance makes up the greater part of wood, 

 vegetable fibre, and the walls of vegetable cells. It is familiar in the form 

 of cotton wool and filtering paper. It is insoluble in water, cold or hot, 

 and is acted upon by dilute acids only in a ver}- slow manner. Strong acids 

 transform it into dextrose. In alkaline solutions it swells up and becomes 

 .semi-transparent. The property of being insoluble in water renders cellu- 

 lose eminently fitted for the purpose to Avhich it is put in nature, namely, 

 to build up the greater part of the framework of the walls of vegetable 

 cells, of vegetable fibres and of wood. 



Its insolubility, however, makes it extremely difficult of digestion in the 

 anima! bowel ; in some mammals it passes through practically unchanged, in 

 others a small percentage is dissolved by the combined action of bacteria 

 and a special ferment. 



The Hemicelluloses differ from true cellulose in that they are not 

 so resistant to solvents, and can be digested a little more readily; more- 

 over they also differ in their chemical composition, for. whilst cellulose 



