THE EXCRETION OF URINE 519 



It may be due in part to vascular changes and in part to reduction in 

 the resistance to filtration brought about by alteration in the permea- 

 bility of the capsule. 



According to the modern theory the polyuria in diabetes is produced 

 by the excessive amount of water taken and by the inability of the 

 kidney to concentrate the urine against the osmotic pressure offered by 

 the concentrated sugar solution in the tubules. The presence of the hy- 

 perglycemia in an amount higher than is present in the optimal blood 

 plasma in this disease makes sugar a nonthreshold substance, so to speak, 

 and none is absorbed. The diuresis following the injection of sugar is 

 therefore of the same type as that produced by sulphate and urea. The 

 diuretic action of the digitalis group is dependent upon its influence on 

 the circulatory system. If the circulation is already sufficient, digitalis 

 does not cause diuresis. The cause of the diuresis produced by pituitary 

 extract is not known. It may be owing in part to its action on the cir- 

 culation and in part to a direct action on the kidney. 



Albuminuria. The plasma proteins ordinarily do not obtain entrance 

 into the tubules of the kidney. In disease such as acute nephritis and 

 cardiac failure, the plasma colloids are filtered off through the capsule, 

 probably because of some change that has occurred in the permeability 

 of its membrane due to inflammation or asphyxia. In these cases the 

 urine is usually reduced in amount. Probably there is no purely glom- 

 erular or tubular type of nephritis, both structures sharing in the dis- 

 ability. While it can not be said that any of the so-called renal tests 

 that have been advanced in recent years are free from criticism, they 

 nevertheless have contributed very useful information. The fact that 

 the kidney of the chronic nephritic excretes a urine of more or less fixed 

 low specific gravity would suggest that here there is an impairment of 

 the resorbing mechanism, and the failure of a kidney to excrete the 

 proper amount of dye, as in the phenolsulphonephthalein test, suggests 

 an impairment in the filtering apparatus. Hard and fast rules can not 

 be applied, however, and probably the tests must at present be inter- 

 preted for the kidney as a whole. 



The Influence of the Nervous System on the Secretion of Urine. In 

 spite of numerous and repeated attempts to demonstrate that a nervous 

 mechanism governs the excretion of urine, no proofs which are above 

 criticism have been forthcoming. Stimulation of the splanchnic nerves 

 results in a diminution in the excretion of urine, probably because of a 

 diminution in the blood supply of the renal vessels owing to the vasocon- 

 striction. Stimulation of the vagus nerves below the level of the cardiac 

 branches has been said to result in the augmentation of the rate of urine 

 excretion (Asher and Pearce 12 ). The results are doubtful, however, since 



