THE DECOMPOSITION OF CARBOHYDRATES 375 



probability a much more important part takes place by the transformation 

 of glycogen into dextrose, which is then carried in . solution by the blood 

 plasma. 



The physiological production of sugar in the liver which was discovered by 

 01. Bernard (1853), has since that time often been denied on the assumption 

 that the increase of sugar easily demonstrated in an excised liver, is due to 

 post-mortem processes. This explanation, however, is not borne out by well- 

 authenticated facts obtained from many experiments; hence the formation of 

 sugar in the liver must be regarded as a physiological process. 



For example, if a puncture in the middle of the floor of the third ventricle 

 between the points of origin of the auditory nerve and the vagus, be made with 

 a blunt needle, sugar immediately appears in the urine (puncture diabetes of 

 Cl. Bernard), and the liver glycogen rapidly disappears. If, however, the 

 puncture experiment be performed on a fasting- animal whose liver glycogen is 

 already used up, no sugar appears in the urine. 



After a time the liver recovers its ability to store up carbohydrates as glyco- 

 gen. On this ground the formation of sugar might be regarded as the result 

 of a stimulus, and not as the result of decomposition. The stimulus is conveyed 

 to the liver by the splanchnics, for after section of these nerves the puncture 

 is ineffective. 



Sugar in the urine can be caused also by stimulation of numerous afferent 

 nerves, as well as by various traumatic and operative effects widely different in 

 character (e. g., concussion or hemorrhage of the brain, inflammation of the 

 brain membranes, neuralgia, etc.). Reflexes are involved here, which, with the 

 cooperation of the medulla, lead to an increased formation of sugar in the liver. 

 By means of these reflexes the working organs, especially the muscles, remove 

 from the liver the carbohydrate fuel required in the performance of their func- 

 tions. They constitute, therefore, as Pfliiger has pointed out, an important 

 regulatory mechanism for the consumption of the available material in the 

 body. 



The transformation of glycogen to sugar is regarded by some authors as an 

 expression of the vital activity of the liver cells; others explain it as the effect 

 of a special enzyme which is formed in the cells. 



After extirpation of the pancreas (cf. page 362), after poisoning with the 

 glucoside phloridzin, in diabetes mellitus, and under certain other circum- 

 stances, the metabolism of the carbohydrates undergoes a chronic change, so 

 that sugar in abnormally large quantities is given off in _ the urine. In 

 phloridzin poisoning this is caused primarily by an increased permeability 

 of the kidneys to sugar, whereas the other forms of morbid glycosuria arise 

 because the body has lost to a greater or less extent the power either to burn 

 sugar or to store it up as glycogen or fat. 



In the so-called light form of diabetes, sugar is given off through the 

 kidneys only in case the food contains carbohydrates; if carbohydrates are 

 prohibited, the loss of sugar ceases. In the severe form of the disease to 

 which pancreatic diabetes belongs, sugar appears in the urine even if no 

 carbohydrates be given in the food. The body then oxidizes little or no sugar, 

 although its power to oxidize is not at all reduced. Since, as was above 

 remarked, at page 128, sugar is probably not formed from fat in the body, 

 the sugar in this case must come from the proteid. 



