THE CHEMICAL COMPOSITION OF THE BODY. 123 



Properties. Monosaccharides are especially soluble and polysaccha- 

 rides are especially insoluble ; monosaccharides and disaccharides do not 

 give colored solutions with iodine while polysaccharides do ; monosaccha- 

 rides and (except saccharose) disaccharides reduce Fehling's solution 

 while polysaccharides do not. 



Of these the most important are : 



Starch (C 6 H 10 OJ, which is contained in nearly all plants, and in 

 many seeds, roots, stems, and some fruits. It is a soft white powder com- 

 posed of granules having an organized structure, consisting of granulose 

 (soluble in water) contained in a coat of cellulose (insoluble in water) ; 

 the shape and size of the granules varying according to the source whence 

 the starch has been obtained. It is not crystalline and will not dialyze. 

 It is insoluble in cold water, in alcohol, and in ether ; it is soluble after 

 boiling for some time, and may be filtered, in consequence of the swelling 

 up of the granulose, which bursts the cellulose coat, and becoming free, 

 is entirely dissolved in water. This solution is a solution of soluble 

 starch or amydin. It gives a blue coloration with iodine, which disap- 

 pears on heating and returns on cooling. It is converted into maltose by 

 diastase, and by boiling with dilute acids into dextrose. 



Glycogen, which is contained in the liver, is also present in all mus- 

 cles but especially in those of very young animals, in the placenta, in 

 colorless corpuscles, and in embryonic tissues. It is sometimes called 

 animal starch and gives many reactions proper to starch itself. It is 

 freely soluble in water, and its solution looks opalescent ; it gives a port- 

 wine coloration with iodine, which disappears on heating and returns on 

 cooling. It is precipitated by basic lead acetate and is insoluble in abso- 

 lute alcohol and in ether. It exists in the liver during life, but very soon 

 after death is changed into sugar. It may be prepared by grinding mus- 

 cle with sand till a pasty mass is formed, boiling the mass in water for 

 twenty minutes, filtering, and then precipitating the glycogen from the 

 filtrate by adding a little more than an equal quantity of 95 per cent al- 

 cohol. It is converted into sugar by diastase ferments, or into dex- 

 trose by boiling with dilute acids. 



Dextrin. This substance is made in commerce by heating dry pota- 

 to-starch to a temperature of 400. It is also produced in the process of 

 the conversion of starch into sugar by diastase, and by the salivary and 

 pancreatic ferments. A yellowish amorphous powder, soluble in water, 

 but insoluble in absolute alcohol and in ether. It corresponds almost ex- 

 actly in tests with glycogen ; but one variety (achroo-dextrin) does not 

 give the port- wine coloration with iodine. 



Cane Sugar, or Saccharose, is contained in the juices of many 

 plants and fruits, and is as a rule extracted from the sugar cane, from 

 beetroot, or from the maple. It is crystalline and is precipitated from 



