THE METABOLISM OF CARBOHYDRATES 905 



liver into glucose. The glucose so formed escapes into the blood, 

 raising the sugar content of this fluid above the normal, and the 

 excess is immediately excreted by the kidneys together with an 

 increased amount of water. The exact manner in which the liver is 

 affected by the puncture cannot be regarded as definitely ascertained. 

 It has been variously explained as due to vasomotor changes in the 

 liver and the flooding of this organ with arterial blood, or to the direct 

 stimulation or paralysis of trophic or secretory fibres passing from the 

 medulla to the liver by way of the vagus nerves. It is possible that 

 the occurrence of sugar in the urine which may occur after head 

 injuries is brought about in a similar way. The glycosuria after 

 operations, administration of anaesthetics, &c., is probably due to a 

 similar disturbance of the glycogen-retaining function of the liver. 



(3) PHLORIDZIN DIABETES. Phloridzin is a glucoside extracted 

 from the root cortex of the apple-tree. It may be decomposed into 

 a sugar and phloretin. When phloridzin or phloretin is administered 

 by the mouth or subcutaneously it gives rise to glycosuria, unaccom- 

 panied, at first at any rate, by any other symptom. The urine may 

 contain from 5 to 15 per cent, of glucose. The glycosuria induced in 

 this way differs from the forms already described in the fact that it is 

 not due to hyperglycaemia. Analysis of the blood shows that the sugar 

 is slightly diminished rather than increased. The excretion of glucose 

 seems to be due to a specific effect of the drug upon the kidneys. If 

 a cannula be placed in the two ureters so as to collect the urine from 

 each kidney separately and a small dose of phloridzin be then injected 

 by a hypodermic syringe into the left renal artery, the urine flowing 

 from the left ureter in two minutes will be found to contain sugar, 

 while the urine from the right kidney will not contain any sugar for 

 another five or ten minutes. The effect therefore is to rapidly drain 

 off sugar from the blood. In order to maintain the sugar content of 

 the blood at its normal height the liver must rapidly manufacture 

 fresh sugar to take the place of that lost by the kidneys. In the first 

 instance the liver will utilise its stored-up glycogen for this purpose. 

 If a dose of phloridzin be given to each of two animals and one animal 

 killed as soon as the excretion of sugar is coming to an end, the liver 

 will be found free from glycogen. If now a second dose of phloridzin 

 be given to the other, which may be regarded as glycogen-free, 

 glycosuria is produced as before, and the excretion of sugar can be 

 continued indefinitely by repeated administration of the drug. So 

 long as sufficient food is given, including carbohydrates, the loss of 

 sugar does not entail any increase in the destruction of the tissues ; 

 but if the drug be administered to starving animals the waste of sugar 

 has to be made good at the expense of material other than carbo- 

 hydrate. The source of the sugar excreted under these circumstances 



