v INTERNAL EESTITUTIYE SECRETIONS 309 



hepatic glycogen by fasting is fed on a diet rich in carbohydrates, 

 the glycogen of the liver is rapidly formed again, and may be 

 present in a considerable quantity a few hours after the meal. 



It is certain that the chief part of the hepatic glycogen is 

 derived from the alimentary carbohydrates. Voit saw that the 

 readily fermentable monosaccharides, both dextrose and laevulose, 

 are converted into glycogen in the liver, either when introduced into 

 the intestine of a rabbit that has fasted for 4 days (and is thus 

 almost destitute of glycogen), or when injected directly but slowly 

 into the circulation. The disaccharides, saccharose and maltose, 

 which ferment less readily, only form glycogen when they are 

 introduced into the intestine, where they are converted into 

 monosaccharides previous to absorption. 



The sugar absorbed from the intestine, carried to the liver, and 

 there converted into glycogen by a process of dehydration and 

 cleavage, prevents hyperglycaemia, or the abnormal increase of 

 blood-sugar which produces glycosuria, i.e. its useless elimination 

 by the kidneys. Pavy noted (1867-69) that slow injection of 

 sugar by one of the veins leading to the portal does not produce 

 glycosuria ; while sugar injected with the same precautions and in 

 the same dose into the jugular vein is partially excreted with the 

 urine. This fact, subsequently confirmed by others, shows that 

 sugar when it goes direct to the liver becomes fixed there in the 

 form of glycogen as a reserve material. Luchsinger (1875) gave 

 direct evidence of this, when he succeeded in increasing the 

 amount of glycogen in a liver recently excised from the body, by 

 irrigating it artificially with blood containing 2 per cent glucose. 



When the amount of sugar introduced with the food is 

 excessive, the liver is no longer able to fix and store it all up in 

 the form of glycogen, so that a certain quantity passes through, 

 and is eliminated by the kidneys (alimentary glycosuria). Accord- 

 ing to Hofmeister, the limit of assimilation of glucose oscillates in 

 the dog between 0'5 and 2 grins, for each kilo, body- weight; bhe limit 

 for saccharose is higher, for lactose lower. For man, according to 

 von Noorden, the limit of assimilation for cane sugar is on an 

 average 200-250 grammes. Unlike sugars, starchy substances 

 never, under normal conditions, produce alimentary glycosuria, 

 either in man or animals, probably because they undergo com- 

 paratively slow digestion in the intestine, so that absorption of 

 the sugar formed, and its passage into the blood, are delayed and 

 take place very gradually. 



Not the whole of the sugar absorbed by the intestine after a 

 diet rich in carbohydrates can be fixed and stored up in the liver. 

 This is evident if we consider the comparatively scanty quantity 

 of glycogen contained in the liver, and reflect that previous to 

 each meal the liver already contains a good store of glycogen, 

 which does not entirely disappear even after several days of fasting. 



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