THE PREPARATION OF THE URINE. 513 



THE PREPARATION OF THE URINE. 



The question has often been raised, whether the urine is really se- 

 creted through the kidney, or whether the urinary constituents are not 

 in part prepared by the kidney itself. The following experiments will 

 shed light upon this subject: 



1. The blood already contains one part of urea in from 3000 to 5000 

 parts ; but the blood in the renal vein contains less urea than that of the 

 artery. This fact indicates that urea is excreted from the blood. 



2. After extirpation of the kidney nephrectomy or ligation of its 

 vessels, urea accumulates in the blood and progressively with the lapse 

 of time to between ^-g- and -g-J-g-. At the same time, fluids containing 

 urea and ammonia are vomited and discharged with the stools. Ani- 

 mals die after such profound operations, moreover, within from one to 

 three days. 



3. If the ureters are ligated, the actual secretion of the kidneys soon 

 ceases. After this, the accumulation of urea in the blood likewise in- 

 creases, and, indeed, as it appears, not in greater amount than after 

 nephrectomy. Nevertheless, it is possible that the kidney, in its meta- 

 bolic activity, does, like other portions of the body, prepare some urea in 

 its tissues. 



4. The blood of birds contains uric acid even under normal con- 

 ditions. Ligation of the ureters, as well as of the renal vessels, or 

 gradual destruction of the secreting renal epithelium by means of 

 subcutaneous injections of neutral potassium chromate, is followed in 

 birds by a deposition of uric acid in the joints and tissues; so that the 

 serous membranes particularly acquire a whitish incrustation there- 

 from. The brain remains free. Also acid combinations of uric acid 

 with ammonia, sodium, and magnesium are thus deposited. Extir- 

 pation of the kidneys in serpents gives rise to the same phenomena in 

 lesser degree. 



From these experiments it may be concluded that the urea, and with 

 it probably most of the organic constituents of the urine, are excreted 

 principally through the kidneys, but are not prepared in them. The 

 seat for the formation of all of these substances is probably to be re- 

 ferred to the tissues. The urea is formed from decomposed proteid, and 

 principally in the liver. As a result of experiments with birds and 

 serpents, v. Schroder and Colasanti come to the conclusion that the 

 formation of uric acid cannot be assumed to take place exclusively in 

 any definite organ. Urobilin is formed from hemoglobin. 



Little is known concerning the physiological-chemical processes in the kidneys 

 themselves. Hippuric acid is formed in part in the kidney, for the blood of 

 herbivora contains no trace thereof; but the synthesis of this substance in rabbits 

 takes place also in other tissues. If blood to which sodium benzoate and glycin 

 have been added is passed through the vessels of a fresh kidney, hippuric acid 

 is formed. If, further, phenol and pyrocatechin are digested with fresh renal 

 tissue, the corresponding sulphuric-acid combinations that occur in the urine are 

 formed. The latter, it is true, are formed also by similar digestion with hepatic 

 and pancreatic tissue and with muscle. From these observations it may be con- 

 cluded that in the body the substances in question are prepared w'ithin the 

 kidneys and the organs named. 



The kidneys are extremely rich in water, and they yield an alkaline reaction. 

 In addition to serum-albumin, globulin, iiucleo-albumin, albumin soluble in sodium 

 carbonate, a gelatin-yielding substance, fat in the epithelial cells (principally after 

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