246 A MANUAL OF VETERINARY PHYSIOLOGY 



The literature of the formation and use of glycogen is extensive, 

 perhaps no substance has given rise to greater controversy ; yet 

 the glycogen story which is accepted to-day is the one originally 

 related by Claude Bernard, who was the discoverer of this singular 

 substance. 



The sugar in the food, and that derived from starch-conversion, 

 finds its way by means of the intestinal vessels into the portal 

 vein, which, depending on the nature of the diet, contains varying 

 proportions of sugar, and from here it passes into the liver ; under 

 ordinary circumstances, it is stored up in the liver as glycogen, 

 being, in fact, reconverted into a kind of starch, and gradually 

 doled out by the hepatic veins to the system as sugar when 

 required. The liver regulates the amount of sugar which should 

 pass into the blood ; so much, and no more, is admitted to the 

 circulating fluid, the amount varying between 0-05 and 0-15 per 

 cent. The sugar in the blood of the ox was estimated by C. Ber- 



AFTER FOOD. 



Fig. 82. — Liver Cells from the Dog during Fasting and after Food 

 (Waller, after Heidenhain). 



During fasting the cells contain no glycogen ; after receiving food they become 

 swollen with this substance. 



nard at 0-17 per cent., in the calf o-i per cent., and in the horse 

 0-09 per cent. There is consequently a great difference between 

 the sugar content of the portal and that of the hepatic vein. 

 When the liver fails to regulate the amount of sugar in the blood 

 diabetes is produced, and this occurs when the amount of sugar 

 rises to more than 0-2 per cent. 



The glycogen which is stored up in the liver for future use 

 may in two or more days be made to disappear by starving and 

 working the animal, the material in this way escaping from the 

 liver as sugar, and passing into the general circulation through 

 the hepatic veins. The administration of arsenic or phosphorus, 

 by their action on the liver cells, also causes a marked diminution 

 in the amount of glycogen, while strychnine in poisonous doses 

 is most effective in this respect, owing to the excessive muscular 

 contractions produced. 



The storing up of glycogen by the liver and its subsequent utili- 

 sation is very closely allied to a similar process in the vegetable 



