520 A MANUAL OF PHYSIOLOGY 



by increasing its production of sugar, the sugar-forming tissues 

 being stimulated to their task either through nervous influences 

 or by chemical messengers circulating in the blood. Why the 

 tissues cannot burn dextrose as they normally do is a question 

 of great interest, but as yet no satisfactory answer can be given. 



Another hypothesis, which endeavours to connect the impair- 

 ment of the glycogenetic function with the impairment of the 

 power to oxidize dextrose, is that it is only sugar which has been 

 condensed or polymerized to glycogen which can be assimilated 

 by the tissues, and therefore burned (v. Noorden) . 



It is remarkable that levulose may within limits be entirely 

 used up in the tissues of a diabetic patient, or of a dog rendered 

 diabetic by extirpation of the pancreas, while dextrose, which i? 

 so closely allied to it, is promptly cast out by the kidneys. 

 Glycogen is also formed from levulose, though not from dextrose, 

 in the depancreatized dog. This is not easily reconciled with 

 the last-mentioned theory unless we suppose that the glycogen 

 which levulose gives rise to is somewhat different from the 

 glycogen produced by the condensation of dextrose. The 

 opposite condition is also seen in a few individuals namely, 

 intolerance of levulose and its spontaneous appearance in the 

 urine (levulosuria) while other carbo-hydrates are normally used 

 up. Like pentosuria (p. 450), the condition is not a serious one. 



In dogs deprived of the pancreas, and in dogs under the 

 influence of phloridzin, glycerin, given by the mouth, causes 

 an increase in the excretion of sugar up to two or three times 

 the original amount. The giving of fat does not increase the 

 amount of sugar excreted, which, however, is increased by such 

 substances as egg-yolk, which contain lecithin. These should 

 accordingly be avoided in cases in which a strictly antidiabetic 

 diet is desired. It is much more important to exclude carbo- 

 hydrates largely or entirely from the food, although oatmeal and 

 potatoes are said to occupy an exceptional position, and have 

 even been recommended as beneficial. Calcium chloride has 

 been stated to diminish the sugar excretion in diabetes (Boigey), 

 and it has a similar effect in certain of the artificial glycosurias 

 (Brown, Fischer). 



In many cases even when carbo-hydrates are completely, or 

 almost completely, omitted from the food, sugar, derived from 

 the breaking-down of proteins, and possibly to some extent from 

 fats, still continues to be excreted, although in smaller quantity. 

 Other products of the deranged metabolism of proteins, and 

 especially of fats, such as acetone, aceto-acetic acid, and oxy- 

 butyric acid, may also appear in the urine, or, accumulating in 

 the blood, may, by uniting with its alkalies/seriously diminish the 

 quantity of carbon dioxide which that liquid is capable of carry- 



