CARBOHYDRATES 185 



Alimentary Glycosuria 



When carbohydrates are being digested and absorbed in 

 large amounts, glycosuria follows. The maximum amount 

 of any sugar which can be taken without causing glycosuria 

 is known as the Assimilation-limit of that particular sugar. 

 Considering that the rate of absorption must depend largely 

 upon the degree of motihty of the intestine, the amount 

 of secretion and other variable factors, it is not surprising 

 that the assimilation-Hmit should be subject to wide 

 fluctuations. In spite of this, there are wide differences in 

 the hmit of different sugars. For glucose, for instance, 

 it is about 200 grms., for laevulose 100-150 grms., for lactose 

 100 grms. 



Ahmentary glycosuria is in itself no indication of a 

 profound disturbance of carbohydrate metabohsm. Its 

 occurrence merely signifies that the filtering capacity of 

 the Hver, if one may so put it, is overtaxed. But any 

 material lowering of the assimilation-hmit indicates an 

 impairment of hepatic function. 



Neurogenic Diabetes 



In his search for a nervous influence over the secretion 

 of sugar by the hver, Bernard discovered that glycosuria 

 could be caused by injury to the calamus scriptorius in 

 the floor of the fourth ventricle. This operation he called 

 " diabetic puncture," and the part of the brain so destroyed, 

 the diabetic centre. 



The efferent nervous path is the splanchnic nerve. 

 Glycosuria can be excited reflexly by stimulation of the 

 central end of the vagus and other nerves. Though it is 

 clear from this that the sugar-forming function of the 

 hver is under the control of the central nervous system, it 

 is doubtful whether a diabetic centre in Bernard's sense 

 really exists. Glycosuria can be caused experimentally by 

 injury to the cerebellum, and it occurs frequently in man 

 after head injuries. Apart from trauma, glycosuria is 



