GLYCOGEN; gligco-len (C.H,.O,), was discovered in 1857 by Bernard and was given the name 'animal It belongs to that class of the carbohydrates called the polysac charides; these are convertible into simple car bohydrates when hydrolysed. Glycogen is the reserve carbohydrate of the animal organism in which it appears to take the place of starch, and it is a normal constituent of all develop ing cells. It is found in the livers of most animals to the amount of 10 per cent and to some extent in the muscles and other parts of foetal animals. It is formed by the action of i a ferment on starches, transforming them into sugars which undergo some alteration, becoming less soluble, and are then deposited in the liver and the muscular tissue. This storing of gly cogen takes• place in times of liberal feeding, but it disappears rapidly from the muscles in times of exertion. Glycogen is prepared from finely minced fresh liver, which is thrown into boiling water acidified with acetic acid. The proteins which coagulate are filtered out, and the remaining proteins precipitated from the filtrate with trichloracetic acid. From the re maining filtrate the glycogen is precipitated by adding alcohol. It is purified by resolution and reprecipitating with alcohol. It is ob tained as an amorphous, snow white powder, yielding an opalescent solution with cold water. It does not ferment, nor does it reduce Fehling's solution, and it is not affected by boiling con centrated solutions of the alkalis. Acids hydro
lyse it eventually to dextrose, but it passes through the phases of dextrins and maltose. Diastase also converts it to dextrins and mal tose. The chief interest attaches to the phy siological function of this substance, and the divergent views taken with regard to it by dif ferent writers. Thus it is said to be the sub stance in the liver mainly concerned in . the conversion of starch into sugar. Other phy siologists affirm that no such transformation takes place, there being no proof of the in crease of sugar after the action of the liver; so that at the present time its exact functions are obscure. It has been suggested that the sugars that are taken into the system with the' food are stored up in the liver in the form of glycogen, to be drawn upon subsequently, ac cording to the needs of the system. In cases of diabetes glycogen is found in much larger quantities than usual, and in cases of starvation it is almost wholly absent. It is contained in the white blood corpuscles in very small amount. It is found in oysters to the extent of 3 per cent. It is found also in the cells of certain fungi, and at times in yeast where it may be very abundant, and then quickly disappear.