THE LIVER AND PANCREAS 249 



be formed from some of the end-products of the pancreatic 

 digestion of proteins (p. 255) — viz., the amino-bodies — of which 

 glycin and alanin may be completely converted into dextrose, 

 and glutamic and aspartic acids partly so converted. 



There are a few observers who regard fat as a source of glycogen, 

 and there is some evidence to show that it may contribute, for it 

 has been said that glycerin acts as a sugar former. If this is so 

 the conversion of fat into glycogen, through its splitting up in the 

 intestinal canal into fatty acid and glycerin, would not be a 

 difficult matter. On the other hand, experiment shows that 

 when an animal is fed solely on fat, the glycogen disappears from 

 the liver as quickly as it does in starvation. Nevertheless, it is 

 an interesting fact that during prolonged starvation, even forty 

 to ninety days, the amount of sugar in the blood is practically 

 constant, and its only sources at this time are the proteins and 

 fat of the body. The question is, therefore, very far from being 

 settled. 



The Liver Ferment. — When a liver is rapidly removed from 

 the body of a recently killed animal which has been appro- 

 priately fed, it contains a quantity of glycogen ; if it is allowed 

 to stand the glycogen gradually becomes reduced in amount, 

 and sugar takes its place ; finally all the glycogen disappears. 

 This change is brought about by a diastatic ferment in the liver 

 cells which changes the glycogen into sugar. If the liver on 

 removal from the body be rapidly minced and boiled, the ferment 

 is destroyed, and dextrose is not formed. 



How the Supply of Sugar is Regulated. — We have seen that in 

 the tissues the glycogen in the form of dextrose is oxidised into 

 carbon dioxide and water, resulting in heat and energy. After 

 every meal a store of glycogen accumulates in the liver for 

 subsequent use, and in spite of changes in the amount of diet, 

 difference in the amount of daily work performed, or of heat 

 produced, yet the sugar in the hepatic veins maintains a perfectly 

 regular proportion of from o-i to 0-2 per cent. The means which 

 control the issue of sugar from the liver are very imperfectly 

 known ; they are probably under the influence of both the nervous 

 system and of an internal secretion produced by the pancreas, 

 and the subject will be again considered when the pancreas is 

 dealt with. One thing seems clear — that the liver itself is unable to 

 regulate the amount, and that whenever either the nervous or 

 chemical factors fail, it allows sugar to pass into the blood in a 

 proportion largely over and above that which can be oxidised 

 {hyperglycemia), with the result that it escapes with the urine 

 (glycosuria), constituting the disease known as diabetes. The 

 sugar excreted with the urine is, of course, lost to the system, 

 and constitutes a heavy drain on the body, which in consequence 



