424 EXCRETION OF PIGMENTS. 



arteries. It is evident, then, that Nussbaum's method is not a reliable one for locating the 

 parts of the kidney through which certain substances are excreted. Adami's experiments also 

 give some support to Heidenhain's view, that the glomerular epithelium " possesses powers of a 

 selective secretory nature," for he finds that in frogs, after ligature of the renal arteries, where, 

 of course, the pressure in the glomeruli is just nearly that in the veins, and in the dog after 

 section of the spinal cord, so that the blood -pressure has fallen below 40 mm. Hg, whereby the 

 secretion of urine is arrested, the injection of laky blood causes Hb to appear in the capsules, 

 although there is no simultaneous excretion of water.] 



Excretion of Pigments. Only during very copious excretion does the capsule participate. 

 After the introduction of a large amount of sodic sulphindigotate, and when the experiment 

 has lasted for a long time, the epithelium of the capsule becomes blue. In albuminuria, the 

 abnormal excretion of urine takes place first in the urinary tubules, and afterwards in the 

 capsules, Hb is partly found in the capsules. According to Nussbaum, egg-albumin passes out 

 through the capsule. 



2. Even when the secretion of the ivatery part of the urine is completely arrested, 

 either by ligature of the ureter, or after a very great fall of the blood-pressure in 

 the renal artery, [as after section of the cervical spinal cord], the before-mentioned 

 substances, when injected into the blood, are found in the cells of the convoluted 

 tubules. The injection of urea under these circumstances causes renewed secretion. 

 These facts show that, independently of the filtration pressure, the secretory activity 

 of these cells is still maintained. 



The independent vital activity of the secretory cells of the urinary tubules, which as yet we 

 are unable to explain on purely physical grounds, renders it probable that the tubules are not to 

 be compared to an apparatus provided with physical membranes. This is proved by the follow- 

 ing experiment : Abeles caused arterial blood to circulate through freshly excised living 

 kidneys. A pale urine-like fluid dropped from the ureter. On adding some urea or sugar to 

 the blood, the secretion became more concentrated. Thus, the excised living kidney also 

 excretes substances in a more concentrated form than those supplied to it in the diluted blood 

 streaming through it. J. Munk obtained similar results in excised kidneys with common salt, 

 nitre, caffein, grape-sugar, glycerin, with increase in the amount of urine secreted. The 

 addition of caffein or theobromin to the perfused blood increases the secretion, exciting the 

 secretory cells to greater activity (v. Schrocder). 



Salts and Gases. The vital activity explains why the serum-albumin of the blood does not 

 pass into the urine, while egg-albumin and dissolved haemoglobin readily do so. . Among the 

 salts which occur in the blood and blood-corpuscles, of course only those in solution can pass 

 into the urine. Those which arc united with proteid bodies, or are fixed in the cellular 

 elements, cannot pass out, or at least only after they been split up. Thus, we may explain the 

 difference between the salts of the urine and those of the blood. Similarly, the urine can only 

 contain the absorbed and not the chemically-united gases. 



Ligature of the Ureter. If the secretion be arrested by compression or by ligature of the 

 ureter, the lymph-spaces of the kidney become filled with fluid, which may pass into the blood, 

 so that the organ becomes oedematous, owing to the passage of fluid into its lymph-spaces. 

 The secretion undergoes a change, as first water passes back into the blood, then the sodic 

 chloride, sulphuric, and phosphoric acids diminish, and lastly the urea (C. Ludwig, Max Herr- 

 mann). Kreatinin is still present in considerable amount. There is no longer secretion of 

 proper urine (Ldbcll). 



Non-Symmetrical Renal Activity. It is remarkable that both kidneys do not secrete 

 symmetrically there is an alternate condition of hyperemia and secretory activity on opposite 

 sides ( 100). One kidney secretes a more watery urine, which at the same time contains more 

 NaCl and urea. Von Wittich observed that the secretion of uric acid was not uniform in all 

 the urinary tubules of the same bird. Extirpation of one kidney, or disease of one kidney in 

 man, does not seem to diminish the secretion (Eosenstein). The remaining kidney becomes 

 more active and larger. 



Reabsorption in the Kidney. In discussing the secretion of the kidney, we must attach 

 considerable importance to the variations in the calibre of the renal tubules in their course. 

 Perhaps in the narrowing of the descending part of the looped tubule of Henle there may be 

 either a reabsorption of water, so that the urine becomes more concentrated, or there may be 

 absorption even of albumin, which may perhaps pass through the glomeruli in small amount. 

 [That reabsorption of fluid takes place within the kidney was part of Ludwig's theory, which 

 is practically a process of filtration and reabsorption. Hiifner pointed out that the structure of 

 the kidneys of various classes of vertebrates corresponded closely with the requirements for 

 reabsorption of water. The experiments of Ribbert show that the urine actually secreted in 

 the cortex of the kidney is more watery than that secreted normally by the entire organ. He 

 extirpated the medullary portion in rabbits, leaving the cortical part intact, and in this way 



