52 g TEXT-BOOK OF PHYSIOLOGY 



ministration of ether, curare, the uranium salts, phlorhizin, etc., is generally 

 followed by the elimination of sugar in varying amounts. Of these agents 

 the one generally used for experimental purposes is: 



Phlorhizin. Phlorhizin is a glucosid obtained from the root bark of the 

 cherry, plum and apple tree. It can readily be separated into glucose and 

 phloretin on the latter of which its action depends. If, therefore, either 

 phlorhizin or phloretin be injected subcutaneously or administered by the 

 mouth, sugar very promptly will appear in the urine in amounts varying, 

 with the dosage, from 5 to 15 per cent. This glycosuria is, however, tem- 

 porary, but may be made more or less continuous by repeated injections at 

 least three or four times daily. Coincidently there is a diminution in the 

 percentage of sugar in the blood (hypoglycemia), the opposite condition to 

 that observed in the glycosurias heretofore mentioned. Inasmuch as this 

 deficiency calls for a larger discharge of sugar from the liver this organ and 

 others as well, soon become free of glycogen especially if the animal is 

 deprived of carbohydrate food. As to the manner in which phlorhizin 

 acts to produce glycosuria opinions are divided. On the one hand, experi- 

 mental investigations lead to the conclusion that the seat of action of 

 the phlorhizin is in the kidney itself (whether in the glomerular or in the 

 tubular epithelium is uncertain), in consequence of which the sugar of 

 the blood is permitted to pass, along with other constituents, into the 

 tubules and hence into the urine. As to the change which the kidney 

 structures undergo under the action of phlorhizin not much is known. 

 On the other hand, it has been assumed that ordinarily the sugar is in 

 combination with colloid material in the blood and by reason of this 

 combination cannot pass across the wall of the glomerular blood-vessels. 

 Any uncombined sugar, as is the case in hyperglycemia, will diffuse readily 

 into the urine. Under the influence of phlorhizin the kidney structure 

 is presumed to acquire the power of breaking up this combination setting 

 the sugar free, whereupon it at once diffuses into the urine. When phlor- 

 hizin is administered to an animal living on a meat and fat diet alone, 

 after all sugar has been discharged from the body, sugar still appears in the 

 urine indicating that it must have some other origin than the glycogen of 

 the liver or other tissues. The ratio of the dextrose to the nitrogen in the 

 urine 2.8 to i (Minkowski) or 3.65 to i (Lusk) , a ratio which corresponds 

 to that found in the urine of diabetic patients living on a meat-fat diet, 

 leads to the conclusion that the sugar arises from the metabolism of pro- 

 tein in a manner already alluded to. 



Pituitary Glycosuria. It was discovered by Gushing during his experi- 

 mental and surgical procedures incidental to the removal of the pituitary 

 in whole or in part, that glycosuria frequently develops which, however, 

 gradually passes away. Subsequently it was shown that mechanical or 

 electrical stimulation of the intact posterior lobe gave rise to a similar glycosu- 

 ria provided of course there was a sufficiently large amount of glycogen in 

 the liver. This effect has been attributed to an increased discharge of the 

 internal secretion of the posterior lobe into the cerebro-spinal fluid and finally 

 into the blood, which in some way lowers the assimilation limit of the ani- 

 mal and hence leads to an elimination of sugar (see chapter on Internal 

 Secretion). 



