Physiology and biochemistry in modern medicine . n. Normally the pressure in the renal portal system isnot sufficient to force blood back through the glomerular vessels. Liga-ture of the renal vessels at once results in a suppression of the urine. If the glomerular vessels are perfused with Ringers solution at a THE i:\< OF URINE 515 pressure equal to thai found in the aorta, a considerable flow of fluidmay lie secured from the ureters, hut no fluid is obtained when the renalportal vein is perfused a1 a pressure equal to thai normally present in this vein. Kountree and Geraghty11 fou
Physiology and biochemistry in modern medicine . n. Normally the pressure in the renal portal system isnot sufficient to force blood back through the glomerular vessels. Liga-ture of the renal vessels at once results in a suppression of the urine. If the glomerular vessels are perfused with Ringers solution at a THE i:\< OF URINE 515 pressure equal to thai found in the aorta, a considerable flow of fluidmay lie secured from the ureters, hut no fluid is obtained when the renalportal vein is perfused a1 a pressure equal to thai normally present in this vein. Kountree and Geraghty11 found that phenolsulplioinplit lialeiuadded to the perfusion fluid passed through the renal portal vein, did notcause secretion, hut when urea was added to the perfusate, fluid con-taining the dye was obtained from the ureter. Unfortunately the pres-sure employed in these experiments may have allowed some fluid to heforced backward into the glomerulus, so thai the results may he due tofiltration through the capsule. Renalartery Malpighiancorpuscle. Renal-portal vein Fig. 172.—Uiagram of blood supply of Malpighian corpuscle and of convoluted tubules in amphibian kidney. (Redrawn from Cushny.) It is generally accepted that the proof that the capsule acts as a filteris fairly complete. Unfortunately such decisive experimental facts cannot be offered to prove the assumption that the epithelium of the tubulesreabsorbs the excess of water and salts which are filtered off throughthe capsule. If the modern theory of urine excretion is correct, the cellsof the tubules must not only absorb large amounts of water, but theymust also allow for the reentrance into the blood, either completely orpartially, of certain salts, while they must reject others entirely. We have called attention above to the fact that the glomerular filtrate isvery different from the urine that is finally passed. The urine contains avery high percentage of small molecules, and the proportion in which they 516 THE EXCR
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