GLYCOGEN. 439 



meals this substance is then doled out gradually, arid sent 

 round the Body in the blood. If a liver be cut up two or 

 three hours after removal from the body of a healthy well- 

 fed animal, and thoroughly extracted with water, it will 

 yield much grape sugar. If. on the other hand, a perfectly 

 fresh liver be heated rapidly to the temperature of boil- 

 ing water, and be then pounded up and extracted, it will 

 yield a milky solution, containing little grape sugar, but 

 much glycogen; a substance which chemically has the same 

 empirical formula as starch (C 6 H 10 & ), and in other ways 

 is closely allied to that body. The salivary and pancreatic 

 secretions rapidly convert it into sugar, as they do starch; 

 the elements of a molecule of water being taken up at the 

 same time 



CeHioOs -f H20 = Cell^Oe 

 Glycogen. Water. Glucose. 



'The same transformation is rapidly effected by ferments 

 present in the blood and liver, and hence the first thing to 

 be done in preparing glycogen is to heat the organ at once 

 to a temperature high enough to destroy these ferments. 

 Pure glycogen is a white amorphous inodorous powder, 

 readily soluble in water, forming an opalescent milky solu- 

 tion; insoluble in alcohol, and giving with iodine a red 

 coloration which disappears on heating and reappears on 

 cooling again. 



About four per cent of glycogen can be obtained from 

 the liver of a well-nourished animal (dog or rabbit). This 

 for the human liver, which weighs about 1500 grams (53 oz.), 

 would give about 60 grams (2. 1 oz. ) of glycogen at any one 

 moment. The quantity actually formed daily is, however, 

 much in excess of that, since glycogen is constantly being 

 removed from the liver and carried elsewhere, while a fresh 

 supply is formed in the organ. Its quantity is subject, also, 

 to considerable fluctuations; being greatest about two hours 

 after a good meal, and falling from that time until the next 

 digestion period commences, when it begins to rise until 

 it again attains its maximum. If a warm-blooded ani- 

 mal is starved glycogen disappears from its liver in the 

 course of four or five days. Glycogen is, thus, clearly 



