CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 733 



and not giving rise to sugar by its own decomposition. The sugar 

 which appears in the urine after a dose of this substance seems to 

 come in part at least from the hepatic store of glycogen when 

 that is present ; but the drug will give rise to sugar in the urine 

 of starving animals, from whose livers (and other tissues) glycogen 

 is presumably absent. In such cases the drug appears, in some 

 way or other, to either stir up the hepatic cells to a manufacture 

 of sugar (and this fact is worth remembering in relation to the 

 discussion which we lately entered into (461) as to the nature of 

 the formation of glycogen) or to produce sugar out of some of the 

 other tissues of the body. 



Artificial diabetes is also a prominent symptom of urari poison- 

 ing. This is not due to the artificial respiration, which is had 

 recourse to in order to keep the urarised animals alive ; because, 

 though disturbance of the respiratory functions sufficient to inter- 

 fere with the hepatic circulation may produce sugar in the urine, 

 artificial respiration may with care be carried on without any 

 sugar making its appearance. Moreover, urari causes diabetes in 

 frogs, although in these animals respiration can be satisfactorily 

 carried on without any pulmonary respiratory movements. The 

 exact way in which this form of diabetes is brought about has not 

 yet been clearly made out. 



A very similar diabetes is seen in carbonic oxide poisoning ; 

 and is one of the results of a sufficient dose of morphia, of amyl- 

 nitrite and of some other drugs. 



There can be no doubt that in diabetes, arising from whatever 

 cause, the sugar appears in the urine because the blood contains 

 more sugar than usual. The system can only dispose (either by 

 oxidation, or as seems more probable in other ways) of a certain 

 quantity of sugar in a certain time. Sugar injected into the 

 jugular vein reappears in the urine whenever the injection becomes 

 so rapid that the percentage of sugar in the blood reaches a certain 

 (low) limit. Sugar in the urine means an excess of sugar in the 

 blood. How in natural diabetes that excess arises has not at 

 present been clearly made out. It may be that some forms of 

 diabetes resemble the artificial diabetes just described as resulting 

 from puncture of the medulla, and arise from a too rapid con- 

 version of the hepatic glycogen, or from carbohydrate material 

 failing to be stored up as glycogen, or from an excessive manu- 

 facture of carbohydrate material by the hepatic cells. All forms 

 of diabetes however cannot be satisfactorily explained in this way; 

 and it has been suggested, though adequate proof has not yet been 

 supplied, that the sugar of diabetes is of a peculiar nature and 

 accumulates in the blood because it is unable to undergo those 

 changes, whatever they be, which befall the normal sugar of the 

 blood. We cannot here discuss the subject in detail ; but there is 

 much to be said in favour of the view that the sources of the 

 excess of sugar in the blood may be various, and hence that 



