512 PHYSIOLOGICAL PROCESS OF URINARY SECRETION. 



Disse studied the alterations in the secretory cells during their 

 activity. With the commencement of this activity the cells become 

 larger, and bright areas of the protoplasm, infiltrated with secretion, 

 appear as halos about the nucleus. The discharge of the secretion into 

 the lumen of the tubules takes place through filtration. The brush- 

 border indicates only the empty cell ; it disappears while the cell is being 

 filled with secretion. 



Henle, H. Meckel, Leydig, and Bial observed in snails constituents of the 

 urine (guanin) within the cells of the kidney. 



2. Also when, either after ligation of the ureter or in consequence of 

 marked reduction in blood-pressure in the renal artery (after division 

 of the cervical cord or venesection), urinary water is no longer secreted, 

 the substances named are, nevertheless, after introduction into the 

 blood, seen to pass over into the urinary tubules. Injection of urea 

 likewise again stimulates the secretion. This indicates that the secre- 

 tory activity takes place independently of the filtration-pressure. 



The independent vital activity of the glandular cells of the urinary tubules 

 not explainable by physical processes makes it impossible to consider the glandular 

 tubules as a simple apparatus resembling physical membranes. This is shown 

 also by the following experiment: Abeles permitted the circulation of arterial 

 blood to continue artificially through fresh, living, extirpated kidneys. Pale 

 urinous fluid escaped from the ureter drop by drop. If urea or sugar were added 

 to the circulating blood, the vessels became dilated and the secretion contained 

 the admixed substances in greater concentration. Thus, also the surviving kid- 

 ney excretes, in concentrated form, substances that circulate in the blood in a 

 dilute state. The same observation was made by I. Munk in analogous experi- 

 ments with sodium chlorid, potassium nitrate, caffein, grape-sugar, and glycerin, 

 with an increase in the total amount of the secretion. Addition of caffein or 

 theobromin to the circulating blood induces an increase in the secretion, stimu- 

 lates, thus, the secretory cells themselves to increased activity. The assumption 

 of vital activity alone explains, also, why the serum-albumin of the blood does 

 not pass into the urine, although egg- albumin or dissolved hemoglobin, intro- 

 duced into the blood, does so rapidly. 



Among the salts that occur in the total blood, also in the blood-corpuscles, 

 naturally only those in solution can pass over into the urine. Those that are 

 united to proteids or in the cellular elements cannot pass over, or at least only 

 after decomposition. This fact explains the difference between the salts of the 

 total blood and those of the urine. The urine can, likewise, take up only the 

 gases absorbed into the blood; and not those in chemical combination. 



Should stagnation of the secretion take place in the ureter, as after ligation, 

 and, later, in the urinary tubules, a return of the secretion into the tissue of the 

 kidney and, later, into the blood will be observed. The kidney becomes edem- 

 atous, in consequence of distention of its lymph-spaces. The secretion is altered, 

 inasmuch as, first, water is reabsorbed into the blood; then the sodium chlorid 

 in secretion is diminished, likewise sulphuric acid and phosphoric acid, and, finally, 

 also the urea. Kreatinin will still be present in considerable amount. A true 

 secretion of urine, later on, no longer takes place. 



The circumstance, further, is noteworthy that the two kidneys never secrete 

 symmetrically. The condition is one of alternation in activity and hyperemia. 

 The one kidney secretes a fluid containing a larger amount of water, and, 

 at the same time, more sodium chlorid and urea. It may even be more 

 acid. v. Wittich observed that the excretion of uric acid in the kidneys of 

 birds does not take place uniformly in all of the urinary tubules, but only in 

 varying areas. The extirpation of one kidney or its morbid destruction in human 

 beings does not diminish the secretion. There occurs increased activity, with 

 enlargement of the remaining organ; and this is due to the increased functional 

 demands upon the secretory cells of this kidney. 



