ABSORPTION 355 



glycogen to glucose is generally ascribed to the action of an 

 hepatic diastase. This conclusion is supported by the fact 

 that the liver tissue, after prolonged treatment with alcohol, 

 has an active diastatic action. But (i) fresh liver has no 

 greater diastatic power than any other tissue. (ii) While 

 the conversion of glycogen to glucose in the liver removed 

 from the animal immediately after death, is at a maximum 

 during the first few minutes and gradually decreases, the 

 conversion of glycogen to glucose, under the influence of 

 liver tissue treated with alcohol, gradually reaches a 

 maximum in an hour and gradually wanes, (iii) It has 

 also been shown that the injection of methylene blue, which 

 poisons protoplasm, but does not interfere with the action 

 of enzymes, checks the conversion, and (iv) that stimulating 

 the splanchnic nerves going to the liver increases the 

 conversion of glycogen, without increasing the amylolytic 

 enzyme in the liver and blood. It is therefore possible that 

 the conversion results from chemical changes in the proto- 

 plasm which are controlled by the nerves of the liver. 

 These nerves are derived from the true sympathetic 

 system. 



Carbohydrate Tolerance. — If more sugar is taken than the 

 liver can deal with, it passes on into the general circulation, 

 and is excreted in the urine. Every animal has a certain 

 power of oxidising or of storing sugar. If the carbohydrates 

 are taken as starch instead of sugar, the process of digestion 

 and the slower absorption enables the liver to deal with much 

 larger quantities. The carbohydrate tolerance varies greatly, 

 and even in the same animal it is different under different 

 •conditions. 



Glycosuria. — If the limit of carbohydrate tolerance is 

 overstepped, sugar increases in amount in the blood 

 (glycsemia) and appears in the urine. Glycosuria is produced. 



Glycosuria may be caused in several different ways. 



1. By decreased carbohydrate tolerance — alimentary 

 glycosuria (fig. 160). 



2. When the glycogen stored in the liver is changed to 

 glucose more quickly than is required by the tissues, the 

 glucose may, to a small extent, be again stored in the 



