GLYCOGEN. SUGAR. 61 



When taken into the alimentary canal, starch is rapidly transformed 

 into sugar by the action of the digestive fluids ; and in this form is 

 absorbed into the circulation. 



II. Glycogen, C 6 H 10 5 . 



This is an amylaceous substance of animal origin, corresponding in 

 character with starch derived from the vegetable world. It is found in 

 the livers of all vertebrate animals in the healthy condition, and in the 

 muscles and integument of the embryo of mammalia at an early period 

 of development. It has also been discovered in the oyster and the 

 cockle-shell. Glycogen, so called from its property of producing sugar 

 or glucose, has the same chemical composition as starch, and agrees 

 with it in all its essential characters, except that it is readily soluble 

 in water, and, when treated with iodine, yields a violet-red instead of 

 a blue color. Its watery solution is opalescent, and deviates the plane 

 of polarization strongly to the right, its specific power of rotation for 

 yellow light being about 130. By boiling with a dilute acid it is 

 changed first into dextrine and afterward into sugar. It also under- 

 goes the saccharine transformation when in solution at the temperature 

 of the living body by contact with saliva, the intestinal juices, the sub- 

 stance of the liver, or the serum of the blood. It is the source of the 

 sugar produced in the animal body, as starch is the source of that 

 formed in vegetables. 



Both starch and glycogen, accordingly, are to be regarded as tempo- 

 rary products, destined to undergo further transformation before being 

 used for the purposes of nutrition. In vegetables, the starch which. 

 is abundantly stored up at one period in the cellular tissues is after- 

 ward liquefied and altered into other substances; and although it 

 enters so largely into the composition of the vegetable food of ani- 

 malSj it is converted into sugar during digestion in the alimentary 

 canal. 



III. Sugar. 



The proximate principles designated under this name include a va- 

 riety of substances which have certain well-marked characters, and are 

 of frequent occurrence in both animal and vegetable juices. They are 

 crystallizable and soluble in water, and have, when in solution, a 

 distinctly sweet taste, which, in some varieties, is very highly de- 

 veloped. They are all decomposed by being heated with sulphuric 

 acid; their hydrogen and oxygen being driven off, while the carbon 

 remains behind as a jet-black deposit. In this condition they are said 

 to be carbonized. The proportions in which they occur in various arti- 

 cles of food, according to the tables of Pay en,. Yon Bibra, and a few 

 other observers, are as follows:. 



